148 M. A. Griard on the Genus Entoniscus. 



atavic type by parasitic retrogression have frequently led 

 astray the zoologists who busy themselves solely with taxo- 

 nomy, and sometimes even embryogenists. Starting from 

 this idea, one might be tempted to compare the singular dorsal 

 processes of Entoniscus with the analogous protuberances 

 which are observed in a great number of Crustacea in the 

 zoea-stage. It is a comparison which naturally occurs to the 

 mind ; and I thought it necessary to indicate it in my prelimi- 

 nary communication upon the genus Entoniscus. I have 

 since reflected that more or less similar protuberances occur 

 in a great number of parasitic Crustacea belonging to inferior 

 types, notably among the Copepoda, where evidently they 

 cannot have the same significance. Hence, while calling 

 the attention of zoologists to the remarkable constancy of 

 these appendages in Entoniscus Cavolinii, I do not venture 

 to pronounce in so affirmative a manner upon their true mor- 

 phological value. 



If we pass to the internal anatomy of the Entoniscus, we 

 shall see that it presents nothing particularly remarkable. 

 Compared with the Bopyrus-type, our crustacean has only 

 undergone a considerable reduction of its various systems of 

 organs. 



The tegumentary system, cuticle and dermis is very like that 

 of the other Isopods. It is clothed internally with a muscular 

 layer, which enables the animal to perform rather slow vermi- 

 form movements of contraction. 



The nervous system appears to me to be reduced merely to 

 the cervical and anterior ventral ganglia ; but my researches 

 in this direction are too incomplete to enable me to deny 

 absolutely the existence of the ventral chain. The movement 

 of the abdominal plates even leads me to suppose that this 

 chain does exist. 



The digestive tube commences with a mouth constructed 

 for sucking, and placed at the lower part of two folds in the 

 form of a sucking-cup; the mass in the form of a brain, called 

 the head by Fritz Miiller, is hollowed internally by a cavity, 

 the walls of which are lined with folds and villosities like 

 those in the stomach of the Bopyri. These villosities have 

 already been indicated by Rathke, Cornalia, and Panceri. 

 This is therefore a true gastric cavity ; and this apparatus, as 

 a whole, would be better called cephalogaster. 



The digestive apparatus is then continued by a short 

 straight tube, terminated ca?cally, at the anterior part of 

 which the so-called hepatic cceca open. 



I ha^e sought in vain for a terminal intcrstine comparable 

 to that described by Bucliholz in Jlemioniscus ; I have been 



