103 
blance to one another and to Spher. Leuckartii Sal. from Naples. The Danish forms which 
are taken on animals of the two first and the two last-mentioned genera, deviate quite 
as much from each other as from the exotic forms, and quite as much as the latter deviate 
from each other. In studying a not very large material of specimens taken on two of 
the genera (Cheirocratus and Corophium) it appeared, on the one hand that the hair- 
covering of the females sometimes, but not always, varied very much according to age 
(Salensky already found that the recently hatched females of S. Leuckartii were more hairy 
than the adults), on the other hand that adult, egg-laying females taken on the same species 
(Cheirocratus Sundevalli) also varied much with respect to the quality of their hair-covering 
on the anterior part of their trunk and on the genital area, and to the appearance of tufts 
of hairs on various parts of the ventral side of the head; however, these last-mentioned 
differences seem to be accounted for by the fact that one of the adult specimens had retained 
part of the hair-covering it had had when young. Between adult females taken in the same 
species there was some difference in the distance between the caudal stylets and the genital 
area, still the differences in this area and in the situation of the caudal stylets were much 
smaller in animals taken in the same species than in several of the forms taken in hosts of 
different species. The size of the egg-laying females was very different, varying according 
to the size of the infested species, so that a specimen from Cheirocratus was thrice the 
length of one from Gammaropsis. There was considerably less difference of structure between 
the males of various species than between the females, and much less difference of size. 
Some of the differences found between the males were decidedly of an individual or acci- 
dental nature. These data placed me in the dilemma of either considering all the animals 
I had found as belonging to one species, though a very variable one, infesting animals of 
widely differing families of Amphipoda, and being spread over an immense geographical area, 
or to admit the eight species established here. Future naturalists who will have a much 
larger material at their disposal to throw light on the varieties of individuals taken in the 
same species, and at the same time will have many parasites from hosts of different genera, 
must pronounce the final verdict on this matter. (Perhaps some day it will be possible to 
solve the question, whether parasites from one genus often can infest animals belonging to other 
genera, by cultivating in an aquarium non-infested specimens of the genera that are to be 
examined, together with infested and non-infested animals of another genus; then perhaps it 
will be seen, whether the larvae, which no doubt swim about only a short while, exclusively 
seek specimens of the same species as the host of the mother, or whether they also infest 
and develop themselves on the other genera). Not having found any parasite on Microdeu- 
topus gryllotalpa Costa, I must consider Spher. Leuckartii Sal. as a ninth (to me unknown) 
species. Unfortunately Salensky’s description and figures are far from being sufficiently exact 
in the details with which we are here concerned. If my species were to be united into one, no 
doubt it would have to be under the name of S. Leuckartii, but I will conclude with the remark 
that I consider it rather improbable that such an arrangement would prove to be well-founded. 
