RESPIEATORY ORGANS IN ARANE.E. 
33 
rous short cones (c.), not attached to the dorsal membrane, 
while in the newly added medial portion (s'.) the rods are 
fused with both membranes. 
Herein lies the explanation of the greater thickness of, and 
the larger number of cells in, the ventral wall of the saccules 
in the earlier- stages (fig. 13b) described on p. 29 ; for we 
may assume that the ventral wall secretes the numerous 
minute rods as well as the ventral cuticula of the primary 
chitinous saccules, and that only their dorsal cuticula is con- 
tributed by the doi’sal wall of the saccules. Being in contact 
at first the rods of the ventral cuticula are able to fuse with 
the dorsal cuticula, but at the first moult and all subsequent 
moults the two cuticulas are sepai-ated by the previously 
formed chitinous saccule except along the newly added medial 
and anterior portions. The chitinous saccules first formed are 
cast off at the first moult, but they previously become squeezed 
very thin and are thus difficult to i-ecognise as such. 
At each subsequent moult the saccules are enlarged in the 
way described for the first moult, and since in the medial and 
in the anterior portion of the chitinous saccules at any period 
of life the rods ai’e found soldered to both membranes, I con- 
clude, generally, that this soldered region represents the 
portion that was added at the previous moult. ^ 
My account of the primary chitinous saccules differs from 
that of both Locy and Jaworowski. The first-named author 
(’86) describes and figures the dorsal chitinous membrane of 
each saccule as smooth and the ventral membrane as den- 
tigei'ous, but not united to the dorsal one in the embryo in 
Agelena naevia. In my sections of the embryos of 
A g e 1 e n a 1 a b y r i n t h i c a the two membranes of the primiti ve 
saccules are undoubtedly fused together, exactly as in Attus 
floricola. According to Jaworowski’s description, in the 
' Tlie same appears to he the case in many other spiders, although it 
has liitherto escaped the notice of investigators: so, Argyroneta, 
Drassodes, Lycosa, Philodromus, etc. There is no special reason 
wliy the added region should never have free rods, hence the above 
statement must not be applied too strictly to all spiders. 
VOL. 54, PART 1. — NEW SERIES. 
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