S2 REPORT OF NEW JERSEY STATE MUSEUM. 

 Tribe GymnoplEa. 



Mouth without organs developed for mastication, though mod- 

 ified as an apparatus for the purpose of sucking. Feet various, 

 developed for walking or prehension, partly with branchise, and 

 modified for swimming. Body mostly enclosed, usually almost 

 entirely, in a buckler, consisting generally of one piece, though 

 occasionally of two. 



Besides the families represented in New Jersey limits, so far 

 as known at present, a number of others from the Middle At- 

 lantic and adjacent faunas will doubtless be added with future 

 researches. All but one of the New Jersey families treated below 

 are parasitic, for the most part on fishes, etc. The following 

 interesting remarks concerning these animals are from Dr. C. B. 

 Wilson. ^ 



The problems of parasitism and its attendant degeneration are 

 among the most interesting in the whole realm of ecology, and 

 nowhere can they be studied to any better advantage than among 

 the parasitic copepods. 



We can find here every grade of parasitism and can easily 

 follow the resultant effects in the habits and morphology of 

 the parasites themselves. There are forms like Argulus which 

 not only move about all over the body of their host, but also 

 change frequently from one species of fish to another, and can 

 even leave their host at will and swim about freely, sometimes 

 for several days, before returning. 



Retaining thus completely their powers of locomotion we 

 should not expect, nor do we find in them, any degeneration, 

 but rather such a modification of the various organs especially 

 used in parasitism — e. g., organs for clinging to their host, for 

 piercing after blood, etc., as will the better adapt them to their 

 specific use. 



Then we find forms like Caligus which roam; about freely over 

 their host's body but do not apparently leave it voluntarily, 

 though they can swim well enough when compelled to do so. 



^ Proc. U. S. Nat. Mus., XXV, 1903, pp. 641-642. 



