308 DK. G. H. POWLBE — BISOATAN PLANKTON : 



in haul 27 « would lead to most misleading inferences about the abundance or scarcity 

 of the several species in tlie district. The mesoplanktonic species in particular are in 

 excess of their real proportions because the net passes through so many more f atlioms of 

 mesoplankton than of epiplankton. 



It will be noticed that no attempt has been made to compare the foregoing results 

 with the conclusions of other observers. The reason for this is two-fold. It seems a 

 little dangerous to discuss the earlier faunistic records, because it is in many cases doubt- 

 ful whether two species which Professor Miiller has now satisfactorily separated may 

 not have, hitherto, been reported as one. It ought, however, to have been possible to 

 compare the conclusions obtained by a study of the Biscayan material (for the area and 

 period of the cruise) with the records obtained by the ' Valdivia ' herself. Unfortunately 

 this is only the case to a very limited extent, owing to the fact that closing-nets were 

 used so little by that expedition, as compared with open vertical nets which in many cases 

 were sunk to considerable depths. Such nets, lowered to (say) 500 fathoms, luring up 

 a mixed sample of two or three different faunas from as many " climates " ; they record 

 only the latitude and longitude (which mean nothing to an animal) and a limit of depth 

 (more rarely of temperature), from below which the specimens captured cannot have come. 

 The hauls with the closing-nets would have been more significant if the upper 100 

 fathoms had been studied systematically at the same time, which was not the case. Tor 

 the present, therefore, it is better not to make any comparison between the records of the 

 'Valdivia' and the ' Research.' 



V. MISCELLANEOUS NOTES. 



Proportion of Males to Females. 



If the numbers of the two sexes be expressed as percentages of the total specimens 

 measured, they come out as shown in the table on p. 309. 



Leaving out of consideration for a moment the last two species, it would seem that 

 the females formed 56-64 per cent., males 44-36 per cent., of the specimens of the 

 majority of species : the four exceptions to this — ametra, liaddoni, loricata, and 

 rhyncliena — were represented by so few specimens that we cannot be sure that they are 

 really exceptions. 



But the last two species are on a different footing. I have already hazarded the 

 suggestion that zetesios may possibly prove to be a parthenogenetic form of magna, but 

 as only 20 specimens in all were observed, males may have been missed if present only 

 in small numbers. The ratio between males and females of the fairly abundant globosa, 

 on the other hand, is startling, and recalls the old history of A2ms. The 'Valdivia,' 

 like the ' Research,' captured only one male, though the female occurred in 16 hauls and 

 presumably therefore in some numbers. Miiller (Naples Monograph, p. 175) regards it 

 as possible that parthenogenesis occurs in some marine Ostracods, but it has not been 

 proved for any Halocyprid ; indeed it is difficult to see how it can be " proved " in ar) 

 oceanic species. Supposing the male captured in haul 22 b to be of globosa, and not of 

 some other Halocypris (at least it seems to be of the same species as Miiller's Valdiviun 



