224 



as Bopyrus mysidum and by Buchholz as Leptophryxus mysidis, and Dr. Hoek 

 records it also under the latter name, none of these authors having apparently 

 been aware of the fact that this form had long been recorded by Kreyer 

 as Dajus mysiclis. In more recent times MM. Giard and Bonnier have published 

 in the "Bulletin scientifique de la France" a very exhaustive description of this 

 interesting form, accompanied by excellent figures, and they are indeed highly to 

 be commended, for giving such a full acount, considering that they had only 

 a solitary specimen at their disposal. As I have had an opportunity of examin- 

 ing numerous specimens of this form, I have been enabled to testify the great 

 exactness of the said distinguished French zoologists, and to supplement their ac-. 

 count as regards the development of the species. In the 2 accompanying plates, 

 figures are given not only of the fully grown animal in both sexes, but also of 

 3 different stages of the female, of a young male in the Cryptoniscian stage, 

 and of an embryo in one of the latter stages. The peculiar larval form figured 

 at the bottom of PI. 94 was found in a sample of plankton from Nansen's 

 Expedition. It is figured here, because in the same sample several specimens of 

 the easily recognizable Cryptoniscian stage of Dajus were found, which makes 

 it highly probable that it represents the 1st free larval stage of the pre- 

 sent form. 



Occurrence. — I have taken this form not infrequently from 2 different 

 species of My sis, viz. M. oculata Fabr. and M. mixta Lilljeborg, both collected 

 off the Norwegian coast, the former in Finmark, at Vardo and Vadso, the latter 

 in 2 localities of the Nordland coast. No differences whatever could be detected 

 between the specimens infesting these 2 species of Mysis, and the nominal spe- 

 cies Dajus mixtus Giard & Bonnier ought therefore to be altogether discarded. 

 The parasite is only found on female specimens of the Mysis, being invariably 

 attached to the ventral face of the last segment of the mesosome, turning its 

 head backwards and its ventral face towards the belly of its host, in such a 

 manner that its body is partly inserted between the 2 pairs of incubatory plates 

 which form the marsupial pouch in the Mysis. In no instance, however, 

 had these plates attained their full size in the infested specimens, and it is, 

 indeed, very probable, that the presence of the parasite put a stop to their 

 growth. The male is found clinging to the ventral face of the metasome of the 

 female, and is partly concealed by the lamellae of the anterior pleopoda. In 

 young females the attached male is often found to be still in the Cryptoniscian 

 stage, and I have also occasionally found similar larval individuals, probably be- 

 longing to both sexes, free in the sea, and likewise not infrequently attached 

 firmly to the rudimentary pleopoda of the Mysis. The number of eggs or embryos 



