M. Steenstrup on the genera Pachybdella and Peltogaster. 161 



expense of the others, and forms by itself a spacious pouch with 

 a large opening. From this we might say, that they form a sort 

 of transition to Peltogaster and Pachybdella, whose ovisacs might 

 perhaps be represented as resulting from a further development 

 of the single large lamina of Bopijrus, and whose feet must then 

 be considered as having disappeared at once from both sides of 

 the body. To this may be added Rathke^s observations, who 

 found the Liriopce, resembling the larvse of Bopyrus, amongst 

 the eggs in the ovisac of Peltogaster Paguri, and Cavolini's 

 observation of the development of Liiiope-Wka larvae from the 

 eggs contained in an irregular sac, which cannot properly be 

 placed far from Packybdella and Peltogaster ; and the question 

 then forces itself upon us, whether we must not suppose that 

 there is an actual and close relationship between these two 

 parasites and the Bopyrida?, and especially whether we must not 

 admit the existence of a more intimate connexion between Pelto- 

 gaster Paguri and its Liriope, than that the latter is parasitic in 

 its ovisac. 



Supposing Peltogaster and Pachybdella to be Bopyridse, the 

 Liriopce might either be regarded as the more advanced larvae of 

 the Peltogaster in which they were found, or as the young state of 

 the male parasite, for it is well known that the males of the 

 Bopyridse are very different from the females and live as parasites 

 upon them. None of these suppositions can however be proved 

 at this moment, unless we are in a position to recognize a re- 

 markable resemblance between the larvse of the Bopyridae and 

 the Crustacean embryos, which Cavolini and Kroyer have found 

 in our parasites. Neither the short notices given by both these 

 authors, nor the figures published by the first, are sufficiently per- 

 fect for this purpose ; but on the other hand, they do not appear 

 to stand in the way of such an opinion. The feet with swim- 

 ming bristles, mentioned by both and represented in Cavolini^s 

 figures, may very well represent the abdominal feet of a Bopyrus ; 

 and even the circumstance that no mention is made of the tho- 

 racic feet which are so characteristic of the Bopyridse, cannot be 

 taken positively as a proof that they were not present, as they 

 might have been so pressed under the belly, that they would 

 only become visible on more careful examination. It even ap- 

 pears from Cavolini's statements about the projecting branchial 

 laminae, seen when the animal was observed from beneath, that 

 he must have seen something, which might be regarded either as 

 these feet, or perhaps as the branchial laminae of the Bopyridae ; 

 nay, we cannot exactly understand how Cavolini can have com- 

 pared his young animals with 0. F. Miiller^s figure of Cancer 

 paludosus, unless they had possessed such feet, or presented quite 



