NO. 1788. NORTH AMERICAN ERGA8ILIDJE— WILSON. 357 



Total length, 1.27 mm. Cephalotliorax, 0.3 mm. long, 0.5 mm. 

 wide. Trunk, 0.75 mm. long, 0.51 mm. wide. Width of the genital 

 segment, 0.25 mm. 



Color the same as in the female. 



{impressus, stamped or marked, in allusion to the pits on the dorsal 

 and ventral surfaces.) 



This species is a fairly common parasite on the southern puffer, 

 Cliilomycterus sclioepfi. It is not found on the gills, however, like 

 most of its near relatives, but on the fins, seeming to prefer the inside 

 of the pectoral fins to any other locality. To these it is fastened so 

 securely that the attempt to remove it usually results in tearing off 

 the maxillipeds which are its organs of prehension. The museum 

 collection includes three lots of specimens, two from Bea,ufort, North 

 Carolina, and one from Woods Hole, Massachusetts, all taken from 

 the same host. The last lot is numbered 38625, the two former ones 

 38627 and 38628, respectively. 



Two points in the morphology of this species are worthy of especial 

 mention. The first is the remarkable increase in the number of eggs, 

 which is accomplished by a corresponding decrease in their size. The 

 egg cases are relatively no larger than those of other species, in fact 

 not as large as some, Ergasilus 7nanicatus, for example. But the eggs 

 are only 0.05 mm. in diameter, and are crowded into the cases as 

 thickly as they can lie. Consequently we find in the wider portions 

 of the cases from 35 to 45 eggs in a cross section, while there about 50 

 in the longest longitudinal rows. This means that each case contains 

 between 1,500 and 2,000 eggs, or from 3,000 to 4,000 in the two cases. 



Such an extraordinary supply of eggs indicates a corresponding 

 loss somewhere in their development, and a careful study of the life 

 history of this species ought to yield some interesting data. 



The other noteworthy fact is a coiling or folding of the intestine. 

 The stomach is elongated within the third and fourth thorax seg- 

 ments, reaches the extreme posterior margin of the latter, and is 

 widest at this posterior end. It then abruptly narrows into the 

 intestine, which is folded back upon itself so as to be cut three times 

 in a single cross section. In the body of the copepod there has been 

 a fusion of the fifth and sixth thorax segments with the abdomen and 

 a marked shortening or telescoping together of these parts. But the 

 intestine has retained its original length and consequently has been 

 thrown back upon itself during the telescoping process. A more 

 complete account of these anomalous conditions will be published 

 later. They also furnish a further incentive to a study of the life his- 

 tory of the species. 



The enlarged figures of the mouth-parts in this and the following 

 species are given without the maxillipeds for the reason that the 

 latter, when in position, hide most of the other appendages, as can 

 be seen in figure 124. 



