71 



last-mentioned cannot be maintained as separate species, but must be considered as one, at 

 any rate this parasite has been taken on two good species of the same genus. But now 

 we come to a remarkable fact, viz. that three adult females have been taken on three 

 specimens of Perioculodes longimanus (Sp. Bate) belonging to a different family altogether, 

 and these females I have not been able to distinguish from those taken in Bathyporeia. If 

 some day the male of the parasite is found in Perioculodes, probably the interesting question 

 will be settled, whether the same parasite can be found in animals belonging to such widely 

 differing families. Mysidion commune I have found on the following three species : Pare- 

 rythrops obesus G. 0. Sars, Erythrops serratus G. O.-Sars and Er. abyssorum G. 0. Sars; 

 moreover, it seems likely that it will be found in some other species of Erythrops living 

 in Norway. Finally, I will state as my opinion that the parasites living on all five Nor- 

 wegian species of the genus Erythrops, belong to the same species: Aspidoecia Normani. 



I will sum up by stating what I consider as an established fact, namely that 

 several species of Choniostomatidse live each on two or more species of the same genus 

 or of two closely related genera, probably even to a considerably greater extent than I 

 have been able to ascertain; perhaps, in exceptional cases, they may be found on animals of 

 different families. On the other hand, I certainly think with regard to several species, that 

 each of them infests only its particular species of hosts, and this result exactly agrees with 

 what is known about the biology of other parasitic families belonging to Arthropoda. Only 

 with regard to Epicaridea, Giard and Bonnier have made the assertion that each parasite has 

 its particular host and is found on no other species, an assertion which I think is incorrect, 

 seeing that this division also comes in under the rule which applies to Choniostomatidse 1 ). 



f. Occurrence together with Parasites of other Orders or Classes. 



In nearly all orders of Malacostraca have been found species of the group or family 

 Epicaridea belonging to Isopoda. Giard and Bonnier have expressed the opinion that 

 there exists a certain connection between Choniostomatidse and Epicaridea; but this objectionable 

 hypothesis I have mentioned above in detail (p. 11 — 12), and at the same time I have stated 

 all I know from my own experience and most of what has appeared in literature about the 

 occurrence of Epicaridea on the species which, according to our present knowledge, are 

 infested by Choniostomatidse, I have written that of Cumacea, Isopoda and Amphipoda 

 together, I have seen about 240 specimens belonging to thirty-eight different species infested 

 with Choniostoinatidse, but that neither in any of these 240 specimens, nor in any other of 

 the thousands of animals belonging to these thirty-eight species, have I found one single 

 specimen of any Epicarid. In Italy Delia Valle has found two specimens of Ampelisca 



') It may be added here that in my treatment of the Malacostraca from the "Ingolf "expedition I shall 

 give more detailed information about the arctic Epicaridea. 



