68 



the marsiipium of Isopoda, Cumacea and Mysidacea sometimes, or often, fix themselves to 

 not full-grown females, I repeat, I cannot tell. 



I will add that in three cases (in Ampelisca tenuicornis, Protomedeia fasciafa from 

 Denmark, and in the same from Greenland) I found in the marsupium, together with one 

 female SphteroneUa without ovisacs (in two cases a male attached to it), four to six of the 

 Amphipod's own eggs, in one case with half-developed young ones. In the marsupium of an 

 Ampelisca ft/pica I found a large female and two ovisacs of SpJuer. microcephala and two 

 of the Amphipod's own eggs. In Eudorella truncatula I found one of its own eggs together 

 with an adult female, three ovisacs and a male; in another specimen were found no less 

 than twenty-four of its own eggs together with an almost adult female and two larvae which 

 were invaders. 



c. Number of Parasites on eaeh particular Host. 



In the systematic part of tliis work I give a kind of statistics of each species, 

 accounting for my findings, and giving numerous data concerning the number of each sex, 

 of the ovisacs and the stages of development found on each particular host. Of this con- 

 siderable material I put down some extracts here, which will give a condensed view of this 

 matter. Of Aspidnecia Normnni which lives fixed on the outside of Erythrops, I have often 

 found one or several females of very difterent sizes on the same host, in one case as many 

 as six females with ovisacs, three younger females and one larva on one single specimen. In 

 a large material of Diask/lit: lucifera with RomoeosceUs minuta in the branchial cavity, I 

 have never found more than one female, as a rule only one male, very seldom two males 

 on one specimen, whereas of Iphinoe trispinom, infested with Horn. medUerranea, only foui' 

 specimens have been thoroughly examined by me ; one of these had two females, six ovisacs and 

 two males in the same branchial cavity, one had an adult and a young female, two ovisacs and 

 a male in the same branchial cavity, one carried a male in one branchial cavity, a female 

 with eight ovisacs and a male in the other. Of the species of Ghoniostoma which live in 

 the branclual cavity of Hippohite, I have found only one specimen of an adult female ou a 

 h<:)St, whereas of younger female parasites one specimen contained three in one branchial 

 cavity, five in the other; in another specimen I saw an empty swelling covering one of the 

 branchial cavities, whereas the other contained one female which was far from half-grown, 

 besides certainly more than fifty larvae and pupae hinged on the gill-flbres; however, I doubt 

 very much whether most of these would have been able to develop themselves into adult 

 females (and perhaps males) on this shi'imp; it seems to me rather doubtful that the animal 

 should be able to afibrd the nourishment required, and still more so whether the pai'asites 

 would find sufficient room to grow. 



In the parasites living in the marsupium we find the greatest differences as to 

 the numbers of them ou one host, but at the same time it must be observed that while 



