3IO DISCOVERY REPORTS 



Shape of trophomeres and gonomeres : Trophomeres conical to cylindrical, gonomeres more or less 

 globular, the distal gonomere often somewhat elongated. 



Number of gonomeres on each trophomere : Up to seven. 



Dimensions of gonomeres: Parasites of Euphausia valle?itini and E. frigida, transverse diameter 

 o- 1 6-0-33 mm.; parasites of E. hemigibba, E. recurva and Thysanoessa gregaria, transverse diameter 

 o- 1 3-0- 1 6 mm. 



Organ of fixation : External part broadened, dividing into the basal parts of the stalks, internal part 

 globular or oval ; the two parts united by a neck which, as a rule, is rather narrow. In a specimen on 

 Th. gregaria the internal part of the organ of fixation has a pointed excrescence directed towards the 

 posterior region of the host. Sieve plate in the lower part of the organ of fixation. 



The data compiled above show that the species of ArnaUocystis can easily be characterized by means 

 of their external parts only. These characters are the following. 



ArnaUocystis fagei Boschma. Trophomeres each with a separate short stalk extending from the 

 external part of the organ of fixation. Trophomeres with rather numerous (up to seven or eight) 

 gonomeres, the latter of globular shape, not more than slightly longer than broad. 



ArnaUocystis racemosiis Coutiere. Trophomeres each with a separate short stalk extending from the 

 external part of the organ of fixation. Trophomeres with rather numerous (up to seven) gonomeres, 

 the latter of oval shape, about twice as long as broad. 



ArnaUocystis fasciatus Page. Trophomeres in tufts of five or six, each tuft with a short stalk attached 

 to the external part of the organ of fixation. Trophomeres with one, rarely with two or three gonomeres ; 

 the latter oval, twice as long as broad or slightly more elongated. 



ArnaUocystis umbeUatiis n.sp. Trophomeres in tufts of ten to twenty, each tuft with a long stalk 

 attached to the external part of the organ of fixation. Trophomeres with two or three (usually three) 

 gonomeres of globular or slightly oval shape. 



ArnaUocystis capiUosiis Fage. Trophomeres with long thin stalks, each more or less separately 

 originating from the external part of the organ of fixation. Trophomeres with one gonomere of 

 cylindrical shape. Gonomeres twice as long as broad or still more elongate. 



Coutiere regarded the specimen mentioned by Bate, the parasite of Pasiphaea cristata Bate, as 

 a representative of his species ArnaUocystis racemosus, parasitic on Pasiphaea tarda Kroyer. The two 

 specimens, indeed, have much in common. Both show approximately the same number of trophomeres ; 

 they are attached to their hosts in approximately the same spot (Bate's specimen on the second ab- 

 dominal segment, Coutiere 's specimen on the third). The number of gonomeres occurring on the 

 trophomeres, however, is different in the two specimens. In Bate's specimen in both of his drawings 

 (Bate, 1888, pi. cxl, figs. 3,3') the trophomeres invariably bear three gonomeres, whilst in Coutiere's 

 specimen this number is variable, up to seven. It is, therefore, not altogether certain that the two 

 parasites really belong to the same species. 



The two specimens of ArnaUocystis wnbeUatus are slightly different. The specimen on Hoplophorus 

 grimaldii Coutiere has a far greater number of trophomeres than the one on H. novae-zeelandiae De Man, 

 though this difference certainly does not point to a specific difference of the two. The host of the 

 larger specimen is about twice the size of the host of the smaller specimen, which may be the reason 

 for the more luxuriant development of the larger specimen. Further, it is not impossible that the 

 smaller specimen had not yet reached its full size. It is of minor importance that the diameter of the 

 trophomeres and the gonomeres in the smaller specimen is smaller than that found in the larger specimen. 



Differences of this kind are of common occurrence in the various specimens of ArnaUocystis fagei. 

 In connexion with the size of the host this species shows a strong variation in the number of the 



