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majority are small, with one or very few genera and rather few species, but the family 
Phoxocephalide is pretty considerable, the family Podoceride is large, and the family 
Lysianasside is exceedingly large (in Sars’ work thirty-three genera), wherefore it seems 
interesting to me that no parasite of our Choniostomatida has been found on any species 
belonging to these families. One species was found in the Mediterranean in the genus 
Microdeutopus Costa, belonging to the Photide, another species has been quite recently 
discovered in Cyclaspis G. O. S., belonging to the family Cumide, and these genera are the 
only two mentioned in the literature of the subject, in which I have not personally observed 
the parasites of this family. To give an account of the forms the examination of which led 
to no result, would be too tedious, neither would it prove much; I will only say that I have 
examined a good number of exotic species, most of which were only represented by a few 
specimens, besides nearly all of the large material our museum possesses of Gammaridea 
from Denmark, Greenland and the Kara Sea, and many of these species were represented 
by from fifty to hundreds of specimens. In F. Meinert’s three papers, of 1877, 1880 
and 1890 respectively, about Danish Malacostraca, and im my own similar papers about the 
fauna of Western Greenland and of the Kara Sea, will be found the names of most of the 
northern and arctic species examined, of which I have had a large material. 
In a later paragraph I shall mention a little more in detail the following pheno- 
menon which stands in a certain connection with the matter above, namely, that of several 
species a considerable material from a large sea can be examined without showing a single 
parasite, whereas sometimes a smaller material of the same species from another sea reveals 
several parasites. This proves that we cannot conclude that a species is not infested, from 
the fact that an investigation of hundreds of specimens from different localities of a certain 
country has not led to the discovery of any parasite. In most cases such examinations must 
be undertaken on a much larger scale than I have been able to do, before any value can 
be attached to the negative results. 
b. Age and Sex of the Hosts. 
It serves our purpose best to divide the hosts into two sections according to their 
parasites, viz. whether the typical residence of these animals is in the marsupium or in other 
places. I will begin by the latter section, repeating my above statement that I only have 
examined five species of parasites which do not live in the marsupiun. 
Aspidoecia Normani, which, as has just been said, lives on the outside of the body 
of species belonging to the genus Evryfhrops, I have found on young specimens as well as 
on adult males and females, but in the latter the marsupium was either empty, or occupied 
by a species of the genus Mysidion. The two species of the genus Choniostoma live in the 
branchial cavity of two species of the genus Hippolyte. From the Kara Sea I have seen 
4) 
