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Hippotyte Gaimardii M.-Edw. I have had a large material from the Kara Sea, and one of 

 similar size from West-Greenland; in the former I only found six infested specimens: four 

 with Choniostoma mirabile, two with Ch. Hansenii; in 'the latter I found none at all, though a 

 few specimens of Ch. Hansenii have been discovered there at least either on H. Gaimardii 

 or on H. polar is. On the latter species I found one Ch. Hansenii from the Kara Sea 

 and one Chon. sp? from the coast of West-Greenland, though H. polaris is not unfrequent 

 in the former, and of common occurrence in the latter locality. This shows distinctly 

 enough that the genus Choniostoma with its two very large and particularly fertile species 

 is pretty scarce in the Kara Sea and rare in West-Greenland. Most of the middle-sized 

 and rather small species of parasites I have found in between very few and about seven 

 specimens of their respective hosts, though my material of the latter was frequently very 

 rich. Only of two parasites: Stenothocheres egregius and Homoeoscelis minuta have I found 

 a great number of specimens in a large material of their respective hosts: Metopa Bruzelii 

 (Goes) and Diastylis lucifera (Kr.). The first-mentioned parasite is the least prolific of all 

 my species, and the second, in this respect, comes nearest to it among the species of which my 

 material of infested hosts was sufficiently large; moreover, the hosts came from several localities. 

 That the number of parasites cannot be determined only by the number of infested hosts, 

 has been proved above, as of some species, e. g. the two afore-mentioned: Stenothocheres 

 egregius and Horn, minuta, we seldom find more than one female and one male on each 

 host, whereas on others we pretty frequently find several females and males as well as 

 pupae in one host, but the only parasite of which, from the last-mentioned reason, I have 

 found as many specimens as of the above-named species, is SphceroneUa paradoxa (living on 

 Bathyporeia, a genus of very frequent occurrence in Denmark); it belongs to the smaller 

 species and, as it seems, does not lay more than four of five ovisacs, which are comparatively 

 large. All these data decidedly point in one direction, but considering the insufficiency of 

 my material, I will take good care not to lay down any rule or law which might possibly 

 not prove quite tenable, and I will content myself with suggesting the direction. We might 

 feel inclined to suppose that the conditions of life of most of these parasites are pretty 

 similar, and that consequently the most prolific species would occur most frequently, the 

 more so, as there is such an enormous difference in their fertility, that a species like Choniostoma 

 mirabile lays at least more than three hundred times as many eggs as StenotJiocheres egregius; 

 however, the above-mentioned examples prove in a striking manner that such a conclusion 

 cannot be drawn. Consequently there must be circumstances to account for the fact that 

 the two least prolific species : Sten. egregius — taken in two localities — and Horn, minuta — 

 taken in several, probably in many places at considerable distance from each other — occur 

 much more frequently than the prolific and very prolific species. An explanation of this 

 fact is required, and I will attempt to explain it, at least partly. No doubt, the critical 

 point in the life of the parasites must be the short period during which the full-grown, 

 though very small, larvaj leave the ovisac and their mother's host in order to seek a new 



