46 DE. G. H. rOWLER — BISCAYAN PLANKTON : 



APPENDIX ON THE DISTRIBUTIOiX OF THE AMPHIPODA AND CLADOCEEA. 



Bij G. Heebeut Fowler, B.A., Ph.D., F.L.S., F.Z.S. 



I. THE AMPHIPODA. 

 When the species captured during the cruise are arranged by hauls, the first thing 

 noticeable is the comparative rarity of the Amphipoda. They occurred in only 68 

 (57 per cent.) of the 118 * " comparable hauls," and were seldom reckoned by more than 

 one or two specimens per haul. 



The various species apparently do not herd together in the way that some organisms 

 {e. g. Chsetognatha) often do; for of these 68 hauls, only one included four species, 

 one three species, thirteen two species, and no less than fifty-three (77 p. c.) produced 

 but a single species. 



In the 68 hauls were 22 species {Eiisirogenes dolichocarpus coming from a " non- 

 comparable " haul) ; of these, no less than twelve (54 p. c.) occurred in one haul only, five 

 (22"7 p. c.) in two hauls, one (45 p. c.) in three hauls, two (9 p. c.) in five hauls, and only 

 two species, both evidently common, occurred in more than five hauls. Tbus, while there 

 are a considerable number of species, the number of individuals is small, except in the 

 two cases mentioned [Hyijerioides longipes and Farathemisto loblivia). 



It is probably due to the fact that Amphipoda are comparatively scarce in these waters 

 that no single species shows any sign of a diurnal vertical oscillation, such as is generally 

 stated to affect the epiplankton, but which, so far as I am aware, has never been definitely 

 demonstrated. I have al o plotted the whole captures of Amphipoda Hyperiidea on to 

 the time-depth tables {cf. pp. 53, 54), but even then can see no certain indication of a 

 nocturnal rise. 



As to the distribution of the individual species recorded elsewhere (even when specialists 

 are agreed upon the nomenclature, which is by no means always the case), it is most 

 di£B.cult to obtain information as to the conditions under which the capture was made, 

 even by comparatively recent expeditions. Most naturalists seem to think that they 

 have done enough if the latitude and longitude are given. But, in every case, at least 

 the time of day, the temperature of the horizon of capture, the kind of net and the depth 

 at which it was worked should be recorded. In cases below (pp. 48, 49) where I have 

 not been able to trace contemporary records of the temperature, I have supplied the 

 mean for the position and depth from Dr. Buchan's ' Challenger ' Report on Oceanic 

 Circulation as the best approximation ; these are marked M. 



* In practice, the nine hauls of the smaU-mouthed net with 180 ineahes per linear inch have been found 

 impossible of fair comparison with the other hauls ; this net caught practically nothing, while the ordinary nets 

 with 60 meshes were catching a good deal. 



