M. A. Giard on the Genus Entoniscus. 147 



The lamellar appendages of the abdomen of onr Entoniscus 

 greatly resemble those which Fritz Miiller has described and 

 figured in E. porcellance. But in the latter the fringed 

 lamina? are situated beneath the thoracic segments, and the 

 abdomen is occupied by sabre-shaped feet. 



In Entoniscus cancrorum Miiller found fringed abdominal 

 folds ; but these folds, much less developed than in E. Cavo- 

 linii, form, on each side of the abdomen, an undulated con- 

 tinuous border, which does not extend so far as to the terminal 

 part of the body. 



From this point of view also, E. Cavolinii therefore differs 

 considerably from the species hitherto described. 



The head, of which we speak last of all, because, of all the 

 external parts of the animal, it is the least visible at the first 

 glance, is concealed beneath the folds of the ovigerous sac, 

 and presents the form of a double sphere (PI. X. figs. 2, 5) . 

 The anterior part, in which the mouth is situated, is furnished 

 with two lamellar folds ; we find no trace of antenna? ; and, 

 by its internal organization, this head should rather have the 

 name of cephalogaster. 



When we free the parasite from its ovigerous sacs and the 

 ova or embryos which they contain, we obtain a body of a 

 pretty constant form, composed in great part of the ovary and 

 the digestive organs of the Entoniscus. 



The ovarian body presents four lateral prolongations, two 

 anterior and two posterior (PL X. fig. 2), which are directed 

 from above downwards, towards the ventral part of the Ento- 

 niscus. We distinguish besides, also on the ventral part, two 

 or three pairs of much smaller eminences, which, with the 

 preceding, perhaps represent the traces of the thoracic feet 

 which have disappeared. Vestiges of these organs are still, 

 in fact, to be seen upon the less degraded animal in the stage 

 represented by figs. 3, 4. 



On the dorsal part we observe two long median protu- 

 berances slightly bent from behind forwards. The posterior 

 is the longer one. 



All these prolongations remind us of those observed in 

 an animal allied to Entoniscus, namely Cryptothiria balani 

 (Hemioniscus, Buchholz), of which I have been able to exa- 

 mine several individuals collected at Wimereux, in the inte- 

 rior of the Balanus balanoides which cover the Tour de 

 Croy. 



It is well known that, in certain species belonging to high 

 groups, parasitism often recalls peculiarities of organization 

 which are only to be met with in the larva? of the other species 

 of the same group. These phenomena of reversion to the 



