Copepoda from the Falkland Islands. 377 



their appearances have at times been frequently noticed, 

 and a considerable time may elapse ere they are again met 

 with. 



The form recorded by Dr. Giesbrecht in his account of 

 the Copepoda collected by the Belgian Antarctic Expedition, 

 already referred to, was obtained in a plankton sample from 

 475 metres, taken in lat. 69° 54' S., long. 82° 49' W. ; only 

 a single specimen was observed. This specimen was a male 

 and is smaller than those from the Falkland Islands, which 

 appear to be all females * ; but although, as previously stated, 

 there is a certain resemblance between the male described by 

 Dr. Giesbrecht and those from the Falklands, 1 am unable, 

 from the differences observed, to regard them as the male 

 and female of the same species. 



C A L I G O I D A. 



Genus Caligus, O. F. Mtiller, 1785. 



Caligus thynni, Dana. (PI. XVI. figs. 13, 14.) 



A single specimen of a Caligus, which appears to be the 

 male of C. thynni, Dana, was captured at Roy Cove, Falkland 

 Islands, in 3 fathoms water, in December 1909. The speci- 

 men measures scarcely 3 mm. from the forehead to the end 

 of the caudal rami, and is therefore considerably smaller 

 than the females of that species are said to be. The males 

 and females of these fish-parasites, however, frequently 

 differ more or less from each other, not only in size, but also 

 in their general appearance. Unless, therefore, both sexe3 

 are available for examination, there may be some difficulty 

 in determining accurately the species they belong to. 

 Figure 13 represents the general form of the specimen seen 

 from the dorsal aspect, and figure 14 one of the fourth pair 

 of legs. It would appear, from records previously published, 

 that the male of C. thynni, like that of C. rapax in our own 

 seas, is able to lead at times the life of a "free swimmer"; 

 hence its occurrence in tow-net gatherings with other pelagic 

 organisms. 



* In this group the males are almost invariably smaller than the 

 females. 



