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now Spheronella Metope, but never both forms in the same specimen. In a large material 
of the same host from another Greenlandish locality appeared a number of specimens of the 
former, not one of the last-mentioned parasites. On specimens of Hippolyte Gaimardii 
M.-Edw. from the Kara Sea appeared now Choniostoma mirabile, now Ch. Hansenii, and 
the latter species was also found in Hipp. polaris (Sab.) from the same sea. In Danish 
specimens of Ampelisca tenuicornis Lilljby. I have found Spharonclla longipes; whereas Giard 
and Bonnier have found in specimens of the same species from le Croisic (Brittany) the 
very deviating Sphar. microcephala. Danish specimens of Protomedeia fasciata Ky. were 
infested with Spher. Giardii, and Greenlandish specimens with the closely related species 
Spher. Bonnieri. On a specimen of Iphinoé trispinosa (Goods.) from Messina Homocoscelis 
mediterranea was found in the branchial cavity and Spheronella marginata in the marsupium. 
In Norwegian specimens of Erythrops serratus G.O. Sars and Prythrops abyssorum G. O Sars 
we not unfrequently find a species of Mysidion in the marsupium, and one or several 
specimens of Aspidoecia Normani on the outside of the body of the same species. In one 
specimen I found two specimens of the latter species on the outside of the body, an adult 
and a young female of Mysidion abyssorum, and a young female of Mys. commune in the 
marsupium, which makes three species of parasites on one animal. 
e. Number of Species of Hosts of the different Parasites. 
The answer to this question presupposes the answer to another, namely that of the 
limitation of the parasitic species, and as this latter question is not treated in detail till 
later on in a separate chapter, I will content myself with mentioning the results of this 
examination, using them in answering the question indicated by the heading. 
Twenty-nine of my species, as a matter of fact, are only found each on one particular 
species. Of the remaining fourteen species eight (belonging to the group of Spher. Leuckartii) are 
also limited each to one particular species; however, it may perhaps be questioned whether these 
eight species can really be maintained as such, or must be regarded as chance varieties of a 
single species (see later on). The remaining six species must be mentioned each separately. 
Choniostoma Hansenii has been ascertained in two species: Hippolyte Gaimardii M.-Kdw. and 
Hippolyte polaris (Sab.). Of Spheronella insignis indeed T have only had a small material which 
was taken on Diastylis cornuta Boeck and Diastylis levis Norm.; however, the difference between 
the parasites of the two species was so slight, that my experiences from other species led 
me to consider them as belonging to one species. The species found by Giard and Bonnier 
on Ampelisca tenuicornis Lilljbg. from le Croisic, which they have described under the name 
of Spher. microcephala, as far as I can see, is identical with the species described by me 
in this work under the same name, and this is taken on Ampelisca typica Sp. Bate in Danish 
waters. Spheronella paradoxa I have found on Bathyporeia norveyica G. O. Sars, Bathyporeia 
pelagica Sp. Bate and B. Robertsonii Sp. Bate, and even if it were proved that the two 
