COPEPODA 783 



of the true copepods, and go through a process of degeneration 

 later. In some the male dies immediately after reaching the Cyclops 

 stage; in others, the male, while highly organized, is very small and 

 lives as a parasite on the body of the female. 



The parasitic Copepoda are much more numerous in salt water 

 than in fresh. In an ordinary examination of fresh-water collec- 

 tions one is not apt to find them, although the male of Ergasilus 

 is occasionally seen. An examination of almost any group of fish, 

 however, will show that they are not at all rare. 



It is a most fascinating study to compare the structure of these 

 degenerate forms with the highly organized free-swimming species, 

 thus finding evidence of the true copepod structure in animals that 

 at first sight would seem to be far removed from the copepods. 

 The structural relationships of these peculiar forms are only im- 

 perfectly understood, so that no satisfactory classification has been 

 made, and, pending more thorough knowledge, all are grouped 

 together, in a somewhat unscientific way, under the term " Siphono- 

 stomata." Although it is well known that these forms are very 

 numerous in the fresh waters of America, the family of the Erga- 

 silidae is the only one which has been studied from a systematic 

 standpoint. Almost total ignorance prevails in regard to the spe- 

 cies of the other families. From the studies in other countries 

 something is known of these families, and it may be assumed that 

 representatives of all of them can be found in American waters. 

 For the sake of completeness of record these families, six in all, 

 will be characterized briefly. 



1. Ergasilidae. These resemble very closely the free-swimming 

 copepods, the general form being much like that of the Cyclopidae. 

 The second antennae are armed at the ends with hooks. On the 

 ventral side of the body of the male there are ordinarily patches 

 of pigment of a deep steel-blue color. The males are free-swimming 

 through the whole period of their lives. The synopsis of the 

 Ergasilidae is adapted from C. B. Wilson. 



Ergasilus is the only genus of this family, and specimens are not 

 unfrequently taken in limnetic collections. They have been found 

 in nearly all parts of the United States. 



2. Caligidae. The body is flat, the caudal part of the abdomen 



