M. Steenstrup on the genera Pachybdella and Peltogaster. 159 



fixed parasitic forms for representations of hermaphroditism, 

 was the principal object of the preceding remarks, in which I 

 have endeavoured to give a better view of our knowledge of 

 these parasites. 



As, however, we have been directing our attention to these 

 shapeless and somewhat enigmatical Crustacea, I will not omit, 

 in conclusion, touching upon the question as to the positive 

 systematic position which they may possibly occupy, in order to 

 remind the reader of one or two remarkable circumstances, 

 which perhaps may not be without their value in the solution of 

 this problem. 



Thus, it is known that in his Peltogaster Paguri, Rathke 

 found some (eight) small Crustacea, scarcely one line in length ; 

 they were in the large cavity which occupied the greater part of 

 the body of the animal, and contained an extraordmary quantity 

 of developed eggs, so that this observer regarded the cavity as a 

 combined digestive and hatching organ. That this cavity, to 

 which the opening at the free end of the body forms an entrance, 

 certainly serves for the latter purpose, we know with certainty 

 from Cavolini^s observations; and these small Crustacea were, 

 therefore, contained in an ovisac (Bruthoble) together with ova 

 in course of development. In the work above quoted, Rathke 

 has described and figured these Crustacea under the new sy- 

 stematic name oi Liriope jnjgmaa ; but, remarkably enough, has 

 regarded this new genus as a form of the Amphipoda, — I know 

 not for what reason, for the characters given do not appear to me 

 to indicate that relation, nor do the figures remind one of an 

 Amphipode. We are rather struck with the great resemblance 

 of the young of the Isopodous genus Bopyrus to these small 

 LiriupcB, and at least one cannot doubt for a moment that the 

 form in question is Isopodous. They appear to difi'er in no 

 essential points from the larvse of the Bopijri which are known to 

 us, especially from the observations of Kroyer and Rathke ; they 

 are only more elongated than the previously described larvse of 

 the Bopyridse. Now, as it is well known that the Bopyri are 

 parasitic under the carapace or abdomen of other Crustacea, we 

 might suppose the relation between the Liriopce and the Pelto- 

 gaster in which they were found, to be of this nature : that the 

 former, instead of serving, as supposed by Rathke, for the 

 nourishment of the Peltogaster, led a parasitic life like other 

 Bopyridffi, in the ovisac of the latter, which, as we are now aware, 

 is a Crustaceous animal. There are, however, other circum- 

 stances which sufficiently prove that the relation may be quite 

 of another nature. 



In the above-mentioned memoir of Cavolini, which is so rich 



