158 BULLETIN OF THE 



The most prominent objects in the anterior chamber, however, are the 

 four big cells which, in two pairs, an anterior and a posterior, fill almost 

 the entire space above the brain, and send their processes ventrad into 

 its substance. They are the cells which Fewkes ('85, Expl. of Plates, 

 p. 208) designates as " ova (1)," and which Biirger ('91, p. 646) sup- 

 posed to be salivary glands. JSieither hypothesis has much in its favor, 

 and I shall present evideiice which I believe shows them to be clearly ner- 

 vous, i. e. ganglion cells. Accordingly, the description of their structure 

 and relations will be deferred until the consideration of the ganglion 

 cells in the brain. 



4. Body Cavity. 



The main body cavity extends from the posterior face of the partition 

 Avhich cuts off the anterior chamber to the extreme posterior end of the 

 body. It varies much in size in different individuals (Plate II. Figs. 23- 

 26, Plate IV. Fig. 58, and Plate VIII. Fig. 96) and can hardly be said 

 to have a definite form. It is smallest in immature individuals, and 

 most capacious after sexual maturity. It differs somewhat from the 

 body cavity of the anterior chamber. The latter, as has been shown 

 already, is lined, in great part at least, by a peritoneal membrane, but the 

 general body cavity shows no trace of such a lining. The protoplasmic 

 ends of the muscle cells terminate at variable depths, thus giving it an 

 irregular boundary, which shows no sign of an endothelium. In the 

 body cavity one finds neither dissepiments nor mesenteries; the intes- 

 tine floats free, or at regular intervals in its course is grown fast to cells 

 in some part of the body wall. 



In the male one always finds a sac more or less developed hanging 

 from the dorsal line, and varying in form and structure. This will be 

 more fully described under the sexual organs, to which it unquestion- 

 ably belongs. 



There is often a small amount of coagulated substance in the body 

 cavity which contains scattered corpuscles similar to those of the ante- 

 rior chamber. They are very pale, entirely unstained, and of a spongy 

 texture. One finds various sizes, and their origin from the protoplasmic 

 ends of the muscle cells has already been maintained. They are by no 

 means abundant, and the amount of coagulum found in the body cavity 

 is also small. In addition to these one always finds in the body cavity 

 of the male free spermatozoa in greater or less numbers. In all of the 

 females obtained the body cavity was nearly or quite filled with eggs. 



