MORPHOLOGY OF THE PEDIPALPI. 31 



in it. By what means the sac is formed and attaclied, I have 

 not been able to find out. It coincides in shape with the 

 abdomen, of wbicb it covers all except the first two segments. 

 The anterior part of it and the sides are thin, but the greater 

 part of the ventral surface is covered by a roughly quadrilateral 

 thicker portion, the margin of which is thicker than the rest. At 

 the posterior end — at least in Phrynus reniformis, in a specimen 

 of which the sac was best preserved — this thickened portion 

 runs out into two short acute triangular processes. This method 

 of carrying the young agrees with what is known of the habits of 

 ThelypJionus. 



As mentioned above, the only embryos of which I liave been 

 able to cut sections are in a comparatively advanced stage of 

 development. One specimen of PArywMsr(SW^/br»^^s,however,in the 

 British Museum was apparently at an early stage (PI. V. fig. 19). 

 In surface view it consisted, as nearly as one could ascertain, of 

 a large cephalic lobe followed by seven or more paired white 

 blocks, extending round about half of the spherical egg. It was 

 evident that only the thicker parts of the embryo were visible, 

 and I take it that the paired blocks are the mesoblastic somites of 

 the embryo, while the cephalic lobe is due to the thickening to 

 form the brain. In the absence of sections, however, any attempt 

 to determine these characters can scarcely be trustworthy. 



The older embryos have already the limbs well developed, and 

 the body has undergone reversion similar to what occurs in Spiders 

 (PI. V. figs. 20 and 21). Just above and a little in front of the 

 base of the fourth pair of limbs is seen a sac-like expansion, the 

 surface of which, as also that of the body and legs in the imme- 

 diate neighbourhood, is covered with a dark layer, apparently 

 formed by the coagulation of some liquid excretion. In section 

 the sac is seen to be hollow, but it was not possible to trace the 

 cavity into connection with that of any other organ. The cuticle 

 covering the sac is peculiar in that it is covered with blunt, 

 conical, hollow processes which I believe are perforated. The 

 cells forming the wall of the sac having drawn away from it 

 owing to preservation, it was impossible to say whether processes 

 from them extend into the cuticular processes or not, but I am 

 inclined to think that such processes existed. 



The presence of this sac was noticed by Bruce *, and a similar 



* Bruce, A. J., "Observations on the Nervous System of Insects," &c. 

 Johns Hopkins University Circulars, vol. vi. 



