20 I'RUCEEDINGS OF THE NATIONAL AIUSEUM. vol. 5a 



Among them all there has not yet been found a true superparasite. 

 They are merely inquilines; that is, none of them use the copepods 

 for anything further than a means of anchorage or support. They 

 all provida their own food, and they neither give anything to nor 

 take anything from the copepods. The food which they take from 

 the water can not affect the copepod in any way, since the latter is 

 sucking thf^ blood of the fish. 



The only influence they can have is a mechanical one, loading the 

 copepod down with a comparatively heavy weight, and increasing 

 considerably the surface of water resistance. 



If they are distributed evenly over the copepod's body they do 

 not affect the torsion, but if there is only a single goose barnacle, or 

 tuft of algae, or colony of hydroids, they must of necessity have 

 more or less influence on torsion according to their position. 



EXTERNAL MORPHOLOGY. 



General body foi'in of adult female. — During the copepodid 

 stages when fertilization takes place the different body regions are 

 as clearly defined as in the Caligidae. Indeed these stages show 

 such a marked likeness to the corresponding ones in the Caligidae 

 as to leave us in no doubt of the close relationship of the two. But 

 as soon as the female has fixed herself to her final host a retrogressive 

 metamorpliosis begins. Horns or processes begin to develop on the 

 sides of the cephalothorax and sometimes [Pennella, Cardlodecfes, 

 Peroderma) over the anterior end. In Peniculus^ Phrixocephalas^ 

 and Collipraviis the anterior thoracic segments remain fairly distinct 

 and each carries a pair of swimming legs. In Lernaea while the seg- 

 ments are fused the swimming legs remain separated by a consid- 

 erable distance and still indicate the thoracic divisions. In the other 

 genera the swimming legs are bunched together close behind the head 

 and there is a corresponding fusion of the thorax segments. The 

 antennae do not increase in size with the growth of the rest of the 

 bod}', but remain minute, and the same is true of the swimming legs; 

 the eyes are buried by the growth of new tissue over them and become 

 invisible, and in some genera {Pennella^ Lernaeolophus) the mouth 

 parts disappear or are possibly represented by small chitin knobs. 



In genei-al, therefore, the body of the Lernaean is unsegmented, 

 but may be more or less distinctly separated into three parts — a 

 cephalothorax made up of the head and one or two anterior thorax 

 segments, a neck or free thorax, and a SAvollen posterior portion or 

 trunk, consisting of the fused genital segment and abdomen. 



In Phrixocephalus the first two thorax segments are fused with 

 the head; in other genera only the first one. The resulting cephalo- 

 thorax is globular in Lemaeocera^ Pennella^ and Lernaeolophus^ 

 while it is more or less flattened dorso-ventrally in Peniculus, Lev- 



