Page:EB1911 - Volume 02.djvu/323

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308
ARACHNIDA
Remarks.—These most strange-looking Arachnids occur in warmer temperate, and tropical regions of Asia, Africa and America. Their anatomy has not been studied, as yet, by means of freshly-killed material, and is imperfectly known, though the presence of the coxal glands was determined by Macleod in 1884. The proportionately enormous chelae (chelicerae) of the first pair of appendages are not provided with poison glands; their bite is not venomous.


1911 Britannica-Arachnida-Galeodes.png

Fig. 66.—Galeodes sp., one of the Solifugae. Ventral view to show legs and somites.

I to VI, The six leg-bearing somites of the prosoma.
opisth 1, First or genital somite of the opisthosoma.
ge, Site of the genital aperture.
st, Thoracic tracheal aperture.
l2, Anterior tracheal aperture of the opisthosoma in somite 2 of the opisthosoma.
l3, Tracheal aperture in somite 3 of the opisthosoma.

a, Anus.






(From Lankester, “Limulus an Arachnid.”)







1911 Britannica-Arachnida-Galeodes2.png

Fig. 67.—Galeodes sp., one of the Solifugae. Ventral view with the appendages
cut off at the base.


I to VI, Prosomatic appendages.
s, Prosomatic stigma or aperture of the tracheal system.
1, First opisthosomatic sternite covering the genital aperture g.
2, Second opisthosomatic sternite covering the second pair of tracheal apertures
sp1.
sp2, The third pair of tracheal apertures.
10, The tenth opisthosomatic somite.
an, The anal aperture.

(Original by Pickard-Cambridge and Pocock.)

1911 Britannica-Arachnida-Galeodes3.png
Fig. 68.—Galeodes sp., one of the Solifugae. Dorsal view.

I to VI, Bases of the prosomatic appendages.

o, Eyes.
a, Lateral region of the cephalic plate to which the first pair of appendages are articulated.
b, Cephalic plate with median eye.
c, Dorsal element of somites bearing third and fourth pairs of appendages.
d, Second plate of the prosoma with fifth pair of appendages.
e, Third or hindermost plate of the prosoma beneath which the sixth pair of
legs is articulated.
1, 2, 9, 10, First, second, ninth and tenth somites of the opisthosoma.

an, Anus.

(Original.)


Galeodes has been made the means of a comparison between the structure of the Arachnida and Hexapod insects by Haeckel and other writers, and it was at one time suggested that there was a genetic affinity between the two groups—through Galeodes, or extinct forms similar to it. The segmentation of the prosoma and the form of the appendages bear a homoplastic similarity to the head, pro-, meso-, and meta-thorax of a Hexapod with mandibles, maxillary palps and three pairs of walking legs; while the opisthosoma agrees in form and number of somites with the abdomen of a Hexapod, and the tracheal stigmata present certain agreements in the two cases. Reference to literature (36).


1911 Britannica-Arachnida-Galeodes4.png

Fig. 69.—Galeodes sp., one of the Solifugae.

I to VI, The six prosomatic e, Third plate of the prosoma-
limbs cut short. carrying appendage VI.
o, The eyes. The prae-genital somite is
b, c, Demarcated areae of the           absent.
cephalic or first 1, First somite of the
prosomatic plate opisthosoma.
corresponding respectively 2, Second do.
to appendages I, II, III, S, Prosomatic tracheal
and to appendage IV (see aperture between legs IV
fig. 68). and V.
d, Second plate of the S′ and S″, Opisthosomatic
prosoma-carrying tracheal apertures.
appendage V. 10, Tenth opisthosomatic
somite.
an, Anus.

(Original.)


1911 Britannica-Arachnida-Garypus litoralis.png

Fig. 70.—Garypus litoralis, one of the Pseudoscorpiones. Ventral view.

I to VI, Prosomatic appendages.
o, Sterno-coxal process of the basal segment of the second appendage.
1, Sternite of the genital or first opisthosomatic somite; the prae-genital somite, though represented by a tergum, has no separate sternal plate.
2 and 3, Sternites of the second and third somites of the opisthosoma, each showing a tracheal stigma.
10 and 11, Sternites of the tenth and eleventh somites of the opisthosoma.

an, Anus.

(Original by Pocock and Pickard-Cambridge.)

1911 Britannica-Arachnida-Garypus litoralis2.png

Fig. 71.—Garypus litoralis, one of the Pseudoscorpiones. Dorsal view.

I to VI, The prosomatic appendages.
o, Eyes.
prae-gen, Prae-genital somite.
1, Tergite of the genital or first opisthosomatic somite.
10, Tergite of the tenth somite of the opisthosoma.
11, The evanescent eleventh somite of the opisthosoma.

an, Anus.

(Original.)


Order 6. Pseudoscorpiones

=

Chelonethi, also called Chernetidia (see figs. 70, 71, 72).—Prosoma covered by a single dorsal shield, at most furnished with one or two diplostichous lateral eyes; sternal elements obliterated or almost obliterated. Appendages of the 1st pair bisegmented completely chelate, furnished with peculiar organs, the serrula and the lamina. Appendages of 2nd pair very large and completely chelate, their basal segments meeting in the middle line, as in the Uropygi, and provided in front with membranous lip-like processes underlying the proboscis. Appendages of the 3rd, 4th, 5th and 6th pairs similar in form and function, tipped with two claws, their basal segments in contact in the median ventral line. The prae-genital somite wide, not constricted, with large tergal plate, but with its sternal plate small or inconspicuous. Opisthosoma