THE CRUSTACEA OF NEW JERSEY. 83 



Here also we should not expect any marked degeneration, but 

 rather a more complete adaptation of the various organs. 



The first evidence of degeneration in this genus lies apparently 

 in the inclination toward free swimming and not so much in the 

 ability to perform it. In these two genera, Argulus and Caligus, 

 the males and females differ but slightly, and in some species of 

 Argulus they may even -be approximately of the same size. The 

 fact that the Argnlidcc do not carry their eggs about with them 

 tends still farther to eliminate the sexual differences, while in 

 the Caligidcc the presence or absence of the long egg pouches 

 with the attendant modifications of structure constitute the chief 

 sexual distinctions. 



Not so, however, in forms like Pandarus, for here both sexes 

 usually fasten themselves in one place and remain there for a 

 long time. They are also so dissimilar in habits and structure 

 that the males have been hitherto placed in an entirely separate 

 genus (Nogagiis), and the two sexes have been proved to belong 

 to the same species only by being repeatedly found in actual co- 

 ition. As is usual in such cases, the female is the more de- 

 generate and can only crawl about slowly; she is so heavy and 

 clumsy that she cannot swim at all. 



Here then is evidence of structural degeneration, not very 

 marked as yet, since fully developed swimming organs are re- 

 tained though they cannot be used in the adult state. 



The male Pandarus, on the contrary, not only retains the loco- 

 motor structures, but can use them, being able to swim about 

 freely whenever occasion demands. 



Again there are forms like Philicthys in which both the male 

 and female have become practically incapable of locomotion, but 

 are still found free in the mucous canals and sinuses of fishes. In 

 them the locomotor organs are markedly degenerate, having 

 dwindled to mere stumps without joints or setae. 



And, finally, we have forms like Chondracanthus, Anchorella 

 and Lernea, in which the female is absolutely incapable of motion, 

 being fixed in one position for life, while the male has dwindled 

 to a mere pigmy, adherent to some part of the female's body. 



