572 PROCEEDINGS OF THE NATIONAL MUSEUM. vol.47. 



free thorax, a genital segment, and an abdomen as in the less degen- 

 erate families. These are separated in the copepodid stages of 

 development, and may then be discerned with comparative distinct- 

 ness. But they are entirely lost in subsequent moults, and the body 

 of the adult female usually shows only two regions, and even these 

 are sometimes (Basanistes) so fused that it is difficult to distinguish 

 them. 



The first region corresponds to the cephalothorax in other copepods, 

 and includes the head with its antennae and mouth parts, the neck, 

 which is sometimes half the entire length or more, and the organs of 

 attachment, the second maxillae. The remainder of the animal is 

 fused together to form the other region, which we may call the trunk 

 and which thus includes the posterior portion of the thorax, the 

 genital segment and the abdomen. 



In the copepodid stages the segmentation of the trunk is distinct, 

 but it gradually disappear with maturity, until it becomes wholly 

 lost in the adult {Clavella, Basanistes), appeal's only in the anterior 

 portion of the trunk (Lernaeopoda) , or is indistinct with a fusion of 

 some of the parts (AcJitheres) . But even in those genera which exhibit 

 the most complete fusion of the body parts the musculature is still 

 broken at regular intervals, each of which indicates a point of 

 segmentation. 



In some species of Salmincola, ClaveUa, etc., there is also a small 

 knob at the posterior end of the trunk, which is well separated from 

 the rest of the body and which has always been called an abdomen. 

 But it is so rudimentary and insignificant when it does appear, and it 

 is so often lacking that it would not be worthy of consideration as a 

 separate body region were it not for the fact that we do fuid well-dif- 

 ferentiated abdomens in the genera Achtheres and NaohrancMa. 

 Accordingly we must determine whether the knob is a true abdomen, 

 corresponding morphologically to those in the two genera just men- 

 tioned or whether it is simply a process. On examining serial sec- 

 tions of Clavella uncinata we find that the anus opens on the posterior 

 end of the trunk, ventral to the base of the process, while the intestine 

 does not enter the process at all. There is an opening at the distal 

 end of the process, and a tube leading through its center. But this is 

 a sperm tube and leads into a sperm receptacle, which is dorsal to the 

 intestine. The outgrowth, therefore, can not in any way be regarded 

 as an abdomen, but is purely sexual in structure and function. And 

 we would propose for it the name of genital process. To this knob 

 the male clings while he fastens the spermatophores on its tip; from 

 these spermatophores the sperms pass into the tube and thence up 

 into the sperm receptacle. As further proof that this is not an abdo- 

 men there are never any anal laminae on it, while they frequently do 

 occur on the posterior end of the trunk (fig. 1). 



