22 FROVEEDlNGti OF TUE NATIONAL MV^EUM. vol. 53. 



The neck or free thorax is usually cylindrical and much narrower 

 than the other two regions; it is sometimes straight {Lernaeenieus 

 and Lernaea) and sometimes flexed {LerTiaeolophus and Eaemoha- 

 ph€s). 



In Peniculu^ it is short and flattened dorsoventrally. while in 

 some species of Pennella it is 100 mm. or more in length. Its length 

 is largely determined by the thiclaiess of the skin and underlying 

 tissue that must be penetrated in order to bring the mouth of the 

 parasite into close contact with some large blood vessel. Even the 

 same species will haA e a longer neck on a thick-skinned and thick- 

 muscled fish like the sunfish and a shorter neck on a thinner-skinned 

 and thinner-muscled fish like the swordfish. The neck often becomes 

 hardened into chitin like the horns and is always much firmer in 

 texture than the following region, especially at the point where it 

 emerges from the skin of the host. 



Usually it is not segmented, the moniliform appearance of such 

 species as Lernaeenieus sprattae being something very distinct from 

 segmentation. 



In Lernaea the neck and body are the same width where they 

 come together, and the point of union is indistinguishable; but the 

 segments are indicated by the attachment of the swimming legs. 

 From these it can readily be seen that all the thorax segments have 

 shared in the elongation of the body. In Peniculus the neck is very 

 much narrower than the body, where the two come together, and is 

 ilistinctiy segmented, with a pair of legs attached to each segment. 

 These show us that while all the thorax segments share in the elonga- 

 tion of the body the .size of the shares increases rapidly from in 

 front backwards. 



hi Leroaeocera and Pennella the swimming legs are found at the 

 anterior end of the neck, packed together as closely as possible just 

 behind the head. This may possibly be a real migration in some of 

 the genera — ^that is, the legs may have moved from the segment 

 where they originally appeared onto preceding segments, as happens 

 lo the maxillipeds in the Lernaeopodidae. But the lengthening of 

 the genital segment during the second free-swimming larval period 

 indicates that the anterior thorax segments contribute very little to 

 the neck and that the great bulk of the latter is made up of the ante- 

 rior end of the fused fifth and genital segments. 



The swollen trunk is made up of the fifth and genital segments 

 and the abdomen, and is much softer in texture than the preceding 

 regions. It is usually greatly elongated as well as swollen, but is 

 larely short and stout. In Lernaeocera and its close relatives it is 

 also convoluted or bent in the form of the letter S. The abdomen is 

 the portion behind the attachment of the ^g^ strings, it is always 



