THE PHYL0C4ENY OF THE TRACHEH: IN ARANEAl. 525 
elongated at the expense of the following segments, being, 
in fact, as long as or longer than the second and third 
segments taken together, so as to bring the spinners to the 
hinder end of the abdomen (text-fig. 2). The positions of 
the spiracles {sp'., sp" .), muscular stigmata (ec. t. 8 and 9, 
representing rudimentary entapophyses to which the longi- 
tudinal muscles are attached), and the genital opening {g. o.) 
are very primitive, at least in all the forms which I have 
been able to examine. All these openings are frequently 
perfectl}’ exposed and separate from each other, especially in 
distended abdomens, as in text-fig. 2. There is at most a 
shallow, open, transverse depression behind the posterior 
edge of the segments, and the skin in this groove behind 
the genital segment is frequently soft and flexible, like the 
soft skin between the hard plates of a segmented body. 
AVhen the abdomen is distended the spiracles and muscular 
stigmata in this soft skin are exposed, but in a contracted 
abdomen (such as that of a female after the deposition of the 
eggs) these openings may become somewhat hidden from 
view owing to the infolding of the flexible skin. Such a 
groove is, however, very different from the typical, deep, 
and more or less rigid infolding found behind the second and 
third abdominal segments in the Pedipalpi (see Tarnani, ’89, 
p. 377, fig. 1, and Lankester, ;04, fig. hh), nearly all arach- 
nomorphous spidei s, and in Liphistius. The longitudinal 
muscles are attached to shallow ectodermal depressions (see 
my paper, ;09, fig. 36), which lie either free or in the larger 
transverse grooves mentioned above, and there are, so far as 
I know, no deep invaginations or ectodermal tendons (enta- 
pophyses) like those found in l*edipalps and arachnomorphous 
spiders. Can this and the absence of interpulmonary folds 
perhaps be a secondary condition in the Mygalomorphas ? 
Or have these folds been acquired independently in the 
Pedipalpi, Liphistius, and Arach no m or ph as ^ ? 
‘ Two interesting drawings by R. I. Pocock are given by Ray 
Lankester (:04. figs. .56 and 64) showing the genital segments of a 
male Thelyphonns assamensis and a female Liphistius de- 
