28 PROCEEDINGS OP THE NATIONAL MVSEUM. vol.53. 



muscles the digestive canal is suspended by connective tissue from 

 the dorsal or lateral walls of the various regions of the body through 

 which it passes. 



The walls of the stomach and intestine also contain both longitu- 

 dinal and transverse muscle fibers, which produce strong peristaltic 

 movements, so that the food is moved about and pushed back and 

 forth over every portion of the digestive epithelium. 



The nervous system. — The copepodid larva has a nervous system 

 almost the same as that of the Caligidae, which has been described 

 in detail elsewhere; but, like the muscular sj^stem, this, too, gradu- 

 ally disappears, and but little of it can be found in the adult female. 

 There is enough of it left, however, to control such movements as 

 persist, and especially the working of the reproductive organs. 



In a median section of the head (fig. C9) the remains of the supra 

 and the infra esophageal ganglia can still be seen, with scattered 

 nuclei representing the nerve centers. Even the nerves themselves 

 may be detected, but only those leading to muscles and organs which 

 are active in the adult. Of the other nerves and even of the ventral 

 chain of ganglia only traces are left, which are difficult to detect. 



In all the genera the tripartite eye of the larva persists in the 

 adult, and there is usually a more or less distinct nerve connecting 

 it with the supra-esophageal ganglion. But it is buried deeply in 

 the tissues over the base of the esophagus and has evidently been 

 covered with tlie surrounding tissues during the growth of the 

 various horns and cephalic processes. The lenses are usually no 

 longer visible and, indeed, the eye itself can not be seen except in 

 specimens which have been cleared in oil or some similar medium. 

 The nervous system, therefore, shows the greatest retrogression of 

 any portion of the body ; it not only fails to increase proportionally 

 to the growth of the body, like the various appendages, but it really 

 diminishes and partially disappears. 



The male reproductive organs. — The male reaches sexual maturity 

 during the fourth copepodid stage, and the sex organs consist of a 

 pair of testes situated in the posterior part of the cephalothorax 

 and separated some little distance from each ether, a pair of straight 

 vaSca deferentia, and a pair of sperm receptacles, containing the 

 spermatophores and located in the genital segment. Each testis is 

 an ovoid or ellipsoid and is somewhat flattened dorsoventrally; the 

 vas deferens leads from the testis directly back alongside the intes- 

 tine and into the genital segment, where it is enlarged into a recep- 

 tacle to hold the spermatophores. In the fifth segment the vas def- 

 erens is convoluted once, and this fold has glandular walls which 

 supply the cement material for the outside covering of the spermato- 

 phores. The opening through which the latter are extruded is on 

 the ventral surface of the genital segment. 



