662 PROCEEDINGS OF THE NATIONAL MVSEVM. vol. xxv. 



would seem fair, therefore, to allow the record to .stand as given, so 

 that this incubation period would ])e a little longer than that of megalops. 



There are othei- considerations also which make it practically certain 

 that the incul)ation period of these two species would be of about the 

 same length, and longer than that of foUdeeus and catostoml (p. 6(50). 



Both Jurine and Claus have given a detailed account of the larva of 

 foUaceus and the various molts through which it passes. 



Claus calls especial attention to the fact that the <Qgg contains a rela- 

 tively large yolk, and that the embryo attains a correspondingly 

 unusual size and advanced development ])efore hatching. This occa- 

 sions the period of increase in the ])rentital development as compared 

 with other parasitic copepods. 



If this be true of folUiceus and catostonii, we would naturally infer 

 that in nugaJopxi and stizostethil^ with their incubating period twice as 

 long, the larva must be even further developed, and such we shall find 

 to be the case. 



In the following account of larval development the facts in relation 

 to foliaceus have been taken from Jurine (1806), Leydig (1850), and 

 Claus (1875), those in regard to stizostethii from Kellicott (1880), while 

 those in reference to catostoml., megalojjs, and (onericamts are from 

 original observations. It is hoped soon to publish a full description 

 of these latter larvw. 



On first issuing from the ^^gg the larvffi of foUaceus and catostoml 

 bear a striking resemblance to a partly developed Caligus, as noted at 

 some length by Claus. 



We find a shield-shaped anterior portion of the body corresponding 

 with the cephalo-thorax in Caligus, three free segments corresponding 

 with the second, third, and fourth thoracic segments in (Jaligus, and a 

 large abdomen carr^dng papilhe armed with seta?, corresponding with 

 the papillated abdomen of the Eucopepods. 



In the larvae of ^1. megalops and ^4. stizostethii the resemblance is 

 not quite so appai'ent, chiefly on account of their more advanced 

 development, but we can still distinguish the same regions easil}^ 

 (Plate VIII.) Hence the nauplius, the metanauplius, and even the 

 earlier cyclops stages are passed by these Argulus larva? inside the 

 egg, and they come forth in one of the more fully developed cyclops 

 stages. All the segments and appendages which are to appear in the 

 adult are present at birth, and in addition the foUaceus and catostoml 

 larvie have extra temporary appendages in the form of a pair of man- 

 dibular palps, which are used as locomotor organs up to the first molt, 

 and then disappear. 



We should expect larvre so very well developed at birth to be much 

 larger than the ordinary crustacean nauplius, and the^^ rather exceed 

 our expectations. The larva of follacem is 0.6 to 0.75 mm. in length, 

 that of catostoml 0.7 to 0.8 mm., while the megalops larva is 0.8 to 



