widely separated from its fellow of the opposite side; 3rd, 4th, 5th and 6th appendages similar in form to the 2nd and to each other. Proboscis free, not supported from below by either the prosternum or the basal segments of the appendages of the 2nd pair. Opisthosoma consisting of only ten somites, which have no tergal and sternal elements, the prae-genital somite contracted to form a waist," as in the Pedipalpi; the last three narrowed to form a

first pair of appendages is provided with a poison gland opening on the fang or terminal segment. Spiders form at least two kinds of constructions snares for the capture of prey and nests for the preservation of the young. The latter are only formed by the female. which is a larger and more powerful animal than the male. Like the scorpions the spiders have a special tendency to cannibalism, and accordingly the male, in approaching the female for the purpose of fertilizing her is liable to be fallen upon and sucked dry by the object of his attentions. The sperm is removed by the male from the genital aperture into a special receptacle on the terminal segment

and IV or barge size IV of Fro and ali lo ang Tsxbosomal FIG. 64-Liphistius desultor. Under side of the uplifted genital or first opisthosomatic somite of the female; g, genital aperture; p. pitted plate, probably a gland for the secretion of adhesive material for the eggs;, the edges of the lamellae of the lung-books of the first pair.

bra brong adlo rasime basa of the 2nd prosomatic appendage. Thus held out at some distance from the body, it is cautiously advanced by the male spider to the genital aperture of the female. Da dimed to stor For an account of the courtship and dancing of spiders, of their webs and floating lines, the reader is referred to the works of M'Cook (30) and the Peckhams (31), whilst an excellent account of the nests of trap-door spiders is given by Moggridge (32). References to systematic works will also be found at the end of this article (33). Order 4. Palpigradi = Microthelyphonidae (see fig. 65). Prosoma covered above by three plates, a larger representing the dorsal elements of the first four somites, and two smaller representing the dorsal elements of the 5th and 6th.

Its ventral surface provided with one prosternal, two mesosternal and one metasternal plate. Appendages of 1st pair consisting of three segments, completely chelate, without poison gland; of 2nd pair slender, leg-like, tipped with three claws, the basal segment without sterno-coxal process taking no share in mastication, and

composed, at least in many cases, of eleven somites, the 11th
somite very small, often hidden within the 10th. Respiratory
organs in the form of tracheal tubes opening by a pair of stigmata
in the 2nd and 3rd somites of the opisthosoma. Intromittent organ
of male beneath sternum of the 1st somite of the opisthosoma.
Sub-order a. Panctenodactyli.-Dorsal plate of prosoma (carapace)
narrowed in front; the appendages of the 1st pair small, much
narrower, taken together, than the posterior border of the carapace.
Serrula on movable digit of appendages of 1st pair fixed throughout
its length, and broader at its proximal than at its distal end; the
immovable digit with an external process.

Family-Cheliferidae (Cheiffer (figs. 70, 71, 72), Chiridium).
Garypidae (Garypus).

Sub-order b. Hemictenodactyli.-Dorsal plate of prosoma scarcely narrowed in front; the appendages of the 1st pair large, not much narrower, taken together, than the posterior border of the carapace o prae gen 123

The serrula or the movable digit free at its distal end, narrowed at the base; no external lamina on the immovable digit.

Family-Obisiidae (Obisium, Pseudobisium)

Chthoniidae (Chthonius, Tridenchthonius). Remarks.The book-scorpions-so called because they were, in old times, found not unfrequently in libraries-are found in rotten wood and under stones. The similarity of the form of their appendages to those of the scorpions suggests that they are a degenerate group derived from the latter, but the large size of the prae-genital somite in them would indicate a connexion with forms preceding the scorpions. Reference to literature (37).

Order 7. Podogona = Ricinulei (see figs. 73 to 76).—Dorsal area of prosoma furnished with two shields, a larger behind representing, probably, the tergal elements of the somites, and a smaller in front, which is freely articulated to the former and folds over the

(Original drawing by Pocock and Pickard-Cambridge.) appendages of the 1st pair. Ventral area without distinct sternal plates. Appendages of 1st pair, bi-segmented, completely chelate. Appendages of 2nd pair, with their basal segments uniting in the middle line below the mouth, weakly chelate at apex Appendages of 3rd, 4th, 5th and 6th pairs similar in form, their basal segments in contact in the middle line and immovably welded, except those of the 3rd pair, which have been pushed aside so that the bases of the 2nd and 4th pairs are in contact with each other. A movable membranous joint between the prosoma and the opisthosoma, the generative aperture opening upon the ventral side of the membrane Prae-genital somite suppressed; the opisthosma consisting of nine segments, whereof the first and second are almost suppressed and concealer! within the joint between the prosoma and the opisthothe following four large and manifest, and the remaining

soma;

three minute and forming a slender generally-retracted tail like that of Thelyphonus. Respiratory organs tracheal, opening by a pair of spiracles in the prosoma above the base of the fifth appendage on IV III 1

FIG. 74. Cryptostemma Karschii. anterior aspect of the prosoma with the "hood" removed. I to IV, first to fourth appendages of the prosoma: a, basal segment of the second pair of appendages meeting its fellow in the middle line (see fig. 75).

(Original drawing by Pocock and
Pickard-Cambridge.)

in West Africa and South America. A fact of special interest in regard to them is that the genus Poliochera, from the Coal Measures, The name Cryptoappears to be a member of the same group. stemma, given to the first-known genus of the order, described by Guérin-Méneville, refers to the supposed concealment of the eyes by the movable Reference to literacephalic sclerite. ture (38).

Order 8. Opiliones (see fig. 77).-Dorsal area of prosoma covered by a single shield usually bearing a pair of eyes. Sternal elements much reduced. Appendages of 1st pair large, three segmented and completely chelate; of 2nd pair either simple and pediform, or prehensile and subchelate; of remaining four pairs, similar in form, ambulatory in function; the basal segment of the 2nd, 3rd and Karschii. Extremity of sometimes of the 4th pairs of appendages the fifth pair of appendfurnished with sterno-coxal (maxillary) ages of the female for lobe. Opisthosoma confluent throughout comparison with that of its breadth with the prosoma, with the the male E in fig. 73. dorsal plate of which its anterior tergal

FIG. 76.-Cryptostemma

plates are more or less fused; at most ten opisthosomatic somites traceable; the generative aperture thrust far forwards between the basal segments of the 6th appendages. Prae-genital somite suppressed. Respiratory organs tracheal, opening by a pair of stigmata situated immediately behind the basal segments of the 6th pair of appendages on what is probably the sternum of the 2nd opisthosomatic somite and also in some cases upon the 5th segment of the legs.

Intromittent organ of male lying within the genital orifice. Sub-order a. Laniatores.-Orifice of foetid glands opening above the coxa of the 4th appendage, not raised upon a tubercle. Orifice of coxal gland situated just behind that of the foetid gland. Sternal plate of prosoma long and narrow, with a distinct prosternal element underlying the mouth. Coxae of 4th, 5th and 6th appendages immovable. Appendages of 2nd pair, strong, usually prehensile and spiny Genital orifice covered by an operculum.

Families-Gonoleptidae (Gonoleples, Goniasoma).
Biantidae (Biantes).

Oncopodidae (Oncopus, Pelitnus).

Trioenonychidae (Trioenonyx, Acumontia). Sub-order b. Palpatores.-Orifice of foetid glands opening above the coxa of the 3rd appendage, not raised upon a tubercle. Orifice of coxal gland situated between the coxae of the 5th and 6th appendages. Sternal plate of prosoma usually short and wide, rarely longer than broad; with a larger or smaller prosternal element underlying the mouth. Coxae of 3rd, 4th. 5th and 6th appendages movable

Ischyropsalidae (Ischyropsalis, Taracus).
Nemastomidae (Nemastoma).

Trogulidae (Trogulus, Anelasmocephalus). Sub-order c. Cyphophthalmi (Anepignathi).-Orifice of foetid glands opening on a tubercle situated near the lateral border of the carapace above the base of the 5th appendage. Orifice of coxa! gland probably situated at base of coxa of 5th appendage; sternal plate of prosoma minute or absent; no prosternal element underlying the mouth. Coxae of 5th and 6th, and usually also of 4th appendages immovable. Appendages of 2nd pair weak, pediform, not prehensile. Genital orifice not covered by an operculum.

Families-Sironidae (Siro, Pettalus).
Stylocellidae (Stylocellus).

Remarks on the Opiliones.-These include the harvest-men, sometimes called also daddy-long-legs, with round undivided bodies and very long, easily-detached legs. The intromittent organs of the male are remarkable for their complexity and elaboration. The confluence of the regions of the body and the dislocation of apertures from their typical position are results of degeneration. The Opiliones seem to lead on from the Spiders to the Mites. Reference to literature (39).

Apparently related to the Opiliones are two extinct groups, the Anthracomarti and Phalangiotarbi, which are not known to have survived the Carboniferous period. In the Anthracomarti the

VI

E

D

VI B, Ventral view of the

prosoma and of the first somite of the opisthosoma, with the appendages I to VI cut off at the base; a, tracheal stigma; mx, maxillary processes of the coxae of the 3rd pair of appendages; g,genitalaperture. C, Ventral surface of the prosoma and opisthosoma; a, tracheal stigma; b, last somite. D. Lateral view of the 1st and 2nd pair of appendages. E, Lateral view of the whole body and two Ist appendages, show. ing the fusion of the dorsal elements of the prosoma into a single plate, and of those of the opisthosoma into an imperfectly segmented plate continuous with that of the prosoma. opisthosoma was movably articulated to the prosoma, and consisted of from eight to ten segments furnished with movable lateral plates, the anal segment being overlapped dorsally by a laminate expansion of the preceding segment. The carapace of the prosoma was unsegmented and often bore a pair of eyes. The appendages of the 2nd pair were slender and pediform; those of the 3rd, 4th, 5th and 6th pairs were similar in form and ambulatory in function with their basal segments arranged round a sternal area as in the order Araneae. The best-known genera were Anthracomartus and Eophognus.

In the Phalangiotarbi the appendages resembled those of the Anthracomarti, except that the basal segments of the last four pairs were usually approximated in the middle line leaving a long and narrow sternal area between; and the carapace of the prosoma was unsegmented. The prosoma and opisthosoma were broadly confluent and probably immovably welded together. The opisthosoma consisted of eight or nine segments, whereof the anterior five or six were very short in the dorsal region, and the posterior three exceptionally large with the anal orifice terminal.

Several genera have been established, the best-characterized being Geraphognus and Architarbus.

Order 9. Rhynchostomi - Acari (see fig. 78).-Degenerate Arachnids resembling the Opiliones in many structural points, but chiefly distinguishable from them by the following features:-The basal segments of the appendages of the 2nd pair are united in the middle line behind the mouth, those of the 3rd, 4th, 5th and 6th pairs are widely separated and not provided with sterno-coxal (maxillary) lobes, and take no share in mastication; the respiratory stig. mata, when present, belong to the prosoma, and the primitive segmentation of the opisthosoma has entirely or almost entirely disappeared.

Sub-order a. Notostigmata.-Opisthosoma consisting of ten segments defined by integumental grooves, each of the anterior four

Family-Opilioacaridae (Opilioacarus).

Sub-order b. Cryptostigmata.-Integument hard, strengthened by a continuously chitinized dorsal and ventral sclerite. Tracheae typically opening by stigmata situated in the articular sockets (acetabula) of the 3rd, 4th, 5th and 6th pairs of appendages.

Family Oribatidae (Oribata, Nothrus, Hoplophora). Sub-order c. Metastigmata.-Integument mostly like that of the Cryptostigmata. Tracheae opening by pair of stigmata situated above and behind the base of the 4th or 5th or 6th pair of appendages. Families Gamasidae (Gamasus, Pteroplus).

Argasidae (Argas, Ornithodoros). Ixodidae (Ixodes, Rhipicephalus).

Sub-order d. Prostigmata.-Integument soft, strengthened by special sclerites, those on the ventral surface of the prosoma apparently representing the basal segments of the legs embedded in the skin. Tracheae, except in the aquatic species in which they are atrophied, opening by a pair of stigmata situated close to or above the base of the appendages of the Ist pair (mandibles). Families Trombidiidae (Trombidium, Tetranychus). Hydrachnidae (Hydrachna, Atax). Halacaridae (Halacarus, Leptognathus). Bdellidae (Bdella, Eupodes).

Sub-order e. Astigmata.-Degenerate, mostly parasitic forms approaching the Prostigmata in the development of integumental

FIG. 78.-Holothyrus nitidissimus, one of the Acari; after Thorell. A, Lateral view with appendages III to VI removed, 1, plate covering the whole dorsal area, representing the fused tergal sclerites of the prosoma and opisthosoma; 2, similarly-formed ventral plate; 3, tracheal stigma.

B, Dorsal view of the same animal; II to VI, 2nd to 6th pairs of appendages. The 1st pair of appendages both in this and in C are retracted.

C, Ventral view of the same; II to VI as in B; a, genital orifice; b, anus; c, united basal segments of the second pair of appendages; d, basal segment of the 6th prosomatic appendage of the right side. The rest of the appendage, as also of app. III, IV and V, has been cut away.

sclerites and the softness of the skin, but with the respiratory system absent.

Families Tyroglyphidae (Tyroglyphus, Rhizoglyphus).
Sarcoptidae (Sarcoptes, Analges).

Sub-order f. Vermiformia.-Degenerate atracheate parasitic forms with the body produced posteriorly into an annulated caudal prolongation, and the 3rd, 4th, 5th and 6th pairs of appendages short and only three-jointed. Family-Demodicidae (Demodex).

Sub-order g. Tetrapoda.-Degenerate atracheate gall-mites in which the body is produced posteriorly and annulated, as in Demodex, but in which the appendages of the 3rd and 4th pairs are long and normally segmented and those of the 5th and 6th pairs entirely absent.

Family Eriophyidae (Eriophyes, Phyllocopies). Remarks on the Rhynchostomi.-The Acari include a number of forms which are of importance and special interest on account of their parasitic habits. The ticks (Ixodes) are not only injurious as blood-suckers, but are now credited with carrying the germs of Texas cattle-fever, just as mosquitoes carry those of malaria. The itch-insect (Sarcoptes scabiei) is a well-known human parasite, so minute that it was not discovered until the end of the 18th century, and "the itch" was treated medicinally as a rash. The female burrows in the epidermis much as the female trap-door spider burrows in turf in order to make a nest in which to rear her young. The male does not burrow, but wanders freely on the surface of the skin. Demodex folliculorum is also a common parasite of the sebaceous