358 THE ANATOMY OF IXVERTEBRATED ANIMALS. 



thick and short commissures with an infra-a^sophageal gan- 

 glionic mass, situated in the head ; of three pairs of large 

 coalesced ganglia in the the rax, one for the prothorax, one 

 for the mesothorax, and one for the metathorax ; of six pairs 

 of closely-united smaller ganglia in the abdomen ; and of a 

 set of visceral or stomato-gastric nerves. The several pairs 

 of thoracic and abdominal ganglia are united by double com- 

 missural cords. In the males the commissures which unite 

 the abdominal ganglia are not straight, but are bent, as if it 

 were needful to make allowance for the possible elongation 

 of the abdomen. The supra-oesophageal ganglia give off the 

 nerves to the antennie from their antero-lateral angles ; while 

 their postero-lateral angles are produced into the great optic 

 nerves. Above the margin of each antennary nerve there is 

 a small rounded tubercle which is in immediate relation with 

 the silvery patch which shines through the fenestra on the 

 inner side of the antennary fossa. Beneath this tubercle, 

 and on the inner side of the antennary nerve, arises the root 

 of the stomato-gastric system of nerves. Each root passes 

 forward for a short distance, then turns inward, and in the 

 middle line enters a heart-shaped ganglion situated on the 

 gullet (Fig. 100, c). From this a median cord passes back- 

 ward beneath the brain and enters a ganglion, which is con- 

 nected on each side with two others (6, e). The continuation 

 of the median cord passes back along the tergal w^all of the 

 oesophagus, and where this begins to dilate into the crop 

 ends in a small triangular ganglion {g), whence lateral 

 branches are given off, w4iich can be traced as far as the 

 gizzard. 



The exact form and arrangement of the male organ of 

 generation has only recently been made out. The most con- 

 spicuous of these organs is a mushroom-shaped gland (Fig. 

 99, t) composed of a great number of short c£eca attached to 

 the extremity of the also very short vas deferens. It is 

 lodged in the hinder end of the abdomen, and covers the 

 posterior abdominal ganglion. The contents of the caeca are 

 viscid, granular, and usually brilliantly white. The anterior 

 end of the vas deferens is dilated, and the caeca are arranged 

 in two groups which open into each side of the dilatation. 

 The contents of the vas deferens are also white and viscid, 

 and evidently consist in great measure of the secretion of 

 the caeca. In the adnlt male, however, innumerable sperma- 

 tozoa with straight rod-like heads, and long flagella, are to be 

 found intermingled with the contents of the vas deferens and 



