ECONOMIC RELATIONS, ANATOMY, AND LIFE HISTORY OF GENUS LERN^A. 1 89 



made up of digestive cells of varying lengths, all of which are filled with a digestive fluid 

 containing small black granules, which are so numerous as to cause the black color of 

 the entire canal. 



The nervous system. — The supra-cesophageal ganglion is comparatively small and 

 subtriangular in horizontal outline. (See fig. 64, pi. xiii.) From the dorsal surface of 

 the blunt posterior angle a nerve extends backward to the reproductive organs and the 

 digestive canal, and from the rounded anterior side other nerves go to the antetmae. 



The infraganglion is by far the largest that has thus far been found in any larval or 

 adult copepod, the nearest approach to it being the one in the adult ErgasiUd. It is so 

 wide where it joins the oesophagus as to cover nearly the whole length of the latter and 

 it extends backward into the genital segment. It tapers rapidly at first, shows a large 

 swelUng opposite the bases of the maxillipeds, and then tapers very gradually through 

 the first five and into the sixth thorax segment. No swellings are found in it opposite 

 the bases of the successive pairs of swimming legs, although good-sized nerves are given 

 off to these. It is pierced close to the oesophagus by stout muscles which run from the 

 anterior end of the stomach to the ventral wall of the head. Both ganglia contain a 

 thick outer layer of cells, while the interior is made up of fibers, and the two are distinctly 

 differentiated throughout the entire length of the ganglion. 



These copepodid larvae thus possess relatively the largest and best developed 

 nervous system amongst the parasitic copepods, which is retained by the male throughout 

 the rest of his life. But in the subsequent exaggerated elongation of the thorax of the 

 female after she has attached herself to her final host, this nervous system is pulled out 

 as if it were ductile into longer and narrower parts, and the two ganglia are greatly 

 reduced in size. The outer cellular layer almost entirely disappears, and the infra- 

 ganglion can not be traced beyond the second thorax segment. It looks as if during 

 the great increase in size of the female no more nerve material could be obtained, and 

 so the nervous system of the i-mm. copepodid larva had to be made over to supply the 

 lo-mm. or 15-mm. female. 



The reproductive organs. — The ovaries and testes are paired and are situated in 

 the posterior part of the cephalothorax and the first one or two free segments. They 

 are close to the dorsal body wall above the stomach, and from their anterior end the 

 oviduct or sperm duct, as the sex may be, leads back above the stomach and intestine 

 to the genital segment. 



In the male each testis is spindle-shaped and flattened dorsoventrally ; the posterior 

 end is usually more pointed than the anterior and is attached to the dorsal body wall; 

 from the anterior end the sperm ducts run back to the genital segment, where it is 

 greatly enlarged and forms an ellipsoidal pouch in which the spermatophores are prepared. 

 (See fig. 63, pi. XIII.) 



The walls of the ducts are very thick and glandular, secreting the cement substance 

 which forms the outer covering or wall of the spermatophores. These latter are 

 cyUndrical and oblong with rounded ends and occupy the whole side of the genital 

 segment. (See fig. 63, pi. xiii.) 



In a horizontal section (fig. 64, pi. xiii) one testis is seen to be behind the other, the 

 anterior one occupying the cephalothorax and first free segment, the posterior one the first 

 and second free segments, both of them between the stomach and intestine and the dorsal 

 body wall. Each testis is swollen until it fills nearly the whole width of the body, and 

 in it can be seen the whole spermatogenesis — the large, nucleated sperm mother cells 

 69571°— IS 13 



