294 DISCOVERY REPORTS 



that of the other specimens, this might point to a distinction. For the present, however, this difference 

 seems to be of too httle importance for a specific character, so that I am including the specimens on 

 Thysanoessa in the species Amallocystis fagei. 



On account of lack of sufficient material for comparison, and owing to deficient knowledge of the 

 structure of the Euphausiacea, no attempt was made to determine the influence of the parasites on the 

 sexual characters of the hosts. It may be observed here that all the parasitized specimens of which 



0° QO^ O.-^^-^^^ 



Fig. 5. Amallocystis fagei Boschma on Thysanoessa gregaria G. O. Sars from St. 871. Transverse sections of host. 



Letters as in Fig. i. x 80. 



sections were made are of the female sex. As already remarked above, the ovary of these infested 

 specimens does not give the impression of being rudimentary or decidedly under-developed. It is 

 quite possible, and it is even to be expected, that in normal specimens of the same size the ovary is 

 much more fully developed. In Einarsson's infested specimens of Thysaiwessa inermis and Th. raschii 

 the ovary appeared to be completely disorganized, and these specimens did not show secondary sexual 

 characters (cf. Einarsson, 1945). The differences in the state of development of the ovary in the 

 specimens from the Antarctic as compared to Einarsson's specimens from the region of Iceland may be 

 due to the fact that in the latter as a rule more than one parasite was found on each infested specimen, 

 whilst in the former the parasite very rarely occurs in more than one specimen on one host. 



Amallocystis umbellatus n.sp. 

 Material : 



St. 81 (32° 45' S, 8° 47' W), 18. iv. 1926, net 450 H, depth of net 650-0 m., i ex. on Hoplophorus novae-zeelandiae 

 De Man (Fig. 11). 



^ ^ St. 692 (02" 02' 15" N, 30° 08' W), 9. V. 1931, net TYFB, depth of net 350-0 m., i ex. on H. grimaldii Coutiere. 

 Type specimen (PI. XLI, figs, i, 2, and Figs. 6-9 «, 10). Transverse sections of part of host containing parasite, 

 Delafield's haematoxylin. 



Specific characters. External part consisting of numerous tufts of trophomeres and gonomeres, 

 united with long stalks to the organ of fixation. Parasites of species of Hoplophorus, attached to the 

 ventral surface of the first or second abdominal segment. 



Of the two specimens the larger (the type specimen) was studied in sections, and of the other some 

 particulars of its external part are mentioned below. 



