No.jAOi. PARASITIC COPEPODS—CALIGID.E— WILSON. 665 



legs. The Eurvphorinfi?, on the other hand, have a pair of plates 

 on the dorsal surface of the fourth segment which usually overlap the 

 genital segment. 



The present species has a pair of dorsal plates which start at the 

 groove between the free and genital segments and, in the female, grow 

 backward and forward until they fuse and cover lioth segments. In 

 the male they cover only the genital segment. It would seem at tirst 

 as if this new genus and species should be placed with the Euryphor- 

 inaB by reason of these dorsal plates. But there are several good reasons 

 for placing it here among the Caligina?. 



First the growth and fusion of the dorsal plates is as unlike the con- 

 dition which pertains in the Eur3"phorina^ as it is unlike that in the 

 Caliginffi. No genus in the former subfamily shows such a fusion of 

 plates, nor do we find it until we come to the Pandarinte. But in this 

 latter subfamily the character of the appendages has changed materi- 

 alh^, and we no longer find anything there which resembles the Cali- 

 ginfe. The fusion of the plates then is like I\mdarus, but the detail of 

 the appendages is still like that of Caligus Lepeophtheirus in every 

 particular. 



Again attention has been called in both sexes to the fact that the 

 remains of a frontal filament can still be seen in the bottom of the inci- 

 sion between the frontal plates. 



This shows conclusively that in its development this genus has a 

 stage during which the young are fastened by a frontal filament, 

 exactly like the chalimus of the Caliginje. 



When we come to discuss the development of the Euryphorina? we 

 shall find that they possess no frontal filament but accomplish their 

 attachment in an entirely difl'erent manner. 



The present genus, therefore, in the detail of its appendages and in 

 the difl'erent stages of its development, is very plainly one of the 

 Caligina?, Yet at the same time it possesses a pair of fused dorsal 

 plates, which are developed in a manner similar to that of the Pan- 

 darinpe. 



Hence it is to be classed with the Caligin^e, but regarded as exhibit- 

 ing the first signs of that degeneration in structure and function so 

 plainly shown in the PandarinsB. 



In this first beginning the dorsal plates do not stiffen the bod}'^ 

 enough, nor is their weight suificient, to retard the copepod's freedom 

 of motion. If they should offer an impediment in this direction the 

 increase in the size of the apron of the third legs, which is the chief 

 organ of locomotion, would more than offset it. 



It is an extremely fortunate circumstance that this single lot of 

 parasites includes well-preserved adults of both sexes and tiie young 

 in several stages of development, so that the foregoing points are 

 clearly demonstrated. 



