M. A. Giarcl on the Genus Entoniscus. 149 



unable to find any thing like it. Here, therefore, we have a 

 fresh confirmation of the general law, according to which the 

 more internal a parasite is, the more degraded is its digestive 

 tube. This progressive degradation, which goes on increasing 

 from the genus Bopyrus to attain its maximum in the Ento- 

 nisci, passing through the genera Hemioniscus and Grypto- 

 niscusj reminds us precisely of what is observed in the 

 Diptera of the family CEstrida3, in which the degradation 

 becomes progressively more marked from the cuticolar 

 types to the gastricolar types, passing through the cavicolar 

 forms. 



The hepatic casca (for which I retain this old name, but 

 without wis! ling to prejudge their true physiological part) are 

 certainly homologous with the organs of the same appearance 

 which we meet with in all Isopoda *. 



These cseca form two large lateral sacs which occupy all 

 the thoracic portion and even a part of the abdomen of the 

 Entoniscus ; their internal cavity is very spacious, a3 may be 

 seen from the section drawn in fig. 7. The wall is covered 

 with slight glandular folds, enclosing a brown substance, the 

 aspect of which reminds one of what we have agreed to call 

 liver in invertebrate animals. 



Kowalevsky was the first f to indicate that the racemose 

 hepatic casca described by Rathke \ in Bopyrus (' Icones zooto- 

 mies' of V. Carus, Taf. xi. fig. 1, h) do not open directly into 

 the digestive tube, but that they all open into a common 

 canal, which itself opens at a single point into the stomach, 

 as in the other Isopods. This observation is perfectly correct ; 

 and I have been able to verify it in several species of Bopyrus 

 and Phryxus. All the difference between the hepatic gland 

 of the Bopyri and that of the E?itonisci, therefore, consists in 

 that in the former this gland becomes ramified and acquires a 

 higher degree of differentiation. It may be said to be a dif- 

 ference analogous to that which exists between the simple 

 pulmonary sac of the Amphibia and the complicated lung of 

 Mammalia and Birds. 



The circulatory system consists, in the first place, of a 

 median dorsal vessel, upon the course of which is placed the 

 heart, the beatings of which are very visible through the 

 transparent integument of the animal. There are besides, on 



* Those organs likewise exist in the Cryptonisci, in which I have indi- 

 cated them, mistaking, however, their true relations. There cannot be 

 any connexion between the ovary and these enormous ca>ea which open 

 into the digestive tube. 



t Kowalevsky, ' Entwickelungsgeschichte der Rippenquallen,' Ein- 

 leitung, p. vii, Mem. de l'Acad. de St. Pe'tersb. 1BGG. 



% Hathke, ' De Bopyro et de Nereide.' 

 Ann. dsMag. N. J list. Ser. 5. Vol. iv. 11 



