CHAETOGNATHA 



619 



\—al.c. 



■ga.v. 



consists of diatoms, copepods and larvae of various kinds including 

 fishes, in fact of most of their plank- 

 tonic neighbours. These are seized 

 by the hook-like jaws and swallowed 

 whole. 



The coelom is well developed with 

 a distinct epithelial lining, and it is 

 divided into two halves by a complete 

 median and vertical mesentery, and 

 also by two transverse septa into three 

 chambers corresponding to the head, 

 the trunk and the tail. Of these the 

 head cavity is mainly occupied by the 

 jaw muscles, while in the trunk and 

 tail cavities are developed the ovaries 

 and the testes respectively. l^\iQ ovaries 

 (Fig. 429) are elongated solid organs 

 attached laterally to the body wall. 

 Traversing each ovary on its inner 

 side is a duct with a blind anterior 

 end [oviduct)', this encloses a second 

 duct [sperm pouch) also with a blind 

 anterior end and with indefinite walls, / 



containing sperm derived from an- ' 



other animal. Both ducts open into fn. 



a small bulblike seminal receptacle with \ 



an external aperture just in front of \ 



the second septum. The maturing 

 egg is fertilized by a spermatozoon 

 which passes into the ovary from the 

 second duct and the zygote then passes 

 through the wall of the oviduct and 

 then to the exterior. 



There is a solid testis in each half of 

 the tail cavity and from these sperm 

 mother cells are constantly budded off 

 into the coelom, which is thus filled 

 with sperm in all stages of develop- 

 ment. The sperm passes into vasa jrig. 428. Sagittahexaptera.\en- 

 deferentia, which are long tubes with tralview, X2h- After O. Hertwig. 

 a small internal opening behind the ale. alimentary canal; An. anus; 

 testes and a terminal dilatation, the /": ^^^^^''•''- ^!^^^^^ ganglion; 

 vesicula seminalis , ^\i\ch opens to the ^ol^^\sp:'^'inLluAe^^^^^ 

 exterior. deferens ; v.s. vesicula seminalis. 



■ov. 



od. 



\--ts. 



>—v. s. 



