582 DR. G. H. FOWLER ON THE [June 21, 



It would appear also that the reproduction (throwing off) of 

 sexual forms is periodic, from the following facts : 



The ' Research ' specimens consisted of very numerous fully- 

 grown sexual forms, a few much smaller sexual forms, and a few 

 large ' Pflegethiere." Other observers x have recorded much the 

 same for the same time of year (July, August ). 



Taking this in conjunction with the fact that, in my collections 

 at any rate, sexual specimens of intermediate size, between the 

 less than 5 mm. and the more than 9 mm. specimens, were very 

 scarce, it would appear that the swarms were due to a period of 

 simultaneous throwing off of numerous sexual forms ; their 

 existence and growth being, naturally, only possible when, as 

 Borgert suggests, the conditions of food, temperature, &c. are 

 favourable. 



The above remarks apply to the 'Besearch' collections of 1896. 

 In 1897 we were able to collect on one day only. On this 

 occasion Doliohim was rare at the surface (like everything else), 

 and the bulk of the catch was at a considerable depth. The small 

 specimens were, proportionately to the large, very much more 

 numerous at the surface than in the collections of ] 896 ; the 

 larger forms seemed to have sunk, like almost everything else, 

 under the influence of very cold and somewhat boisterous weather. 

 The following table gives the numbers taken : 



Sta. Haul in fathoms. Temperature. Specimens. 



20 e. 16 large -, 4 small 



20/. 4 



20 g. 40toO ] 25 



20 a. 200 to 100 



206. 300 to 200 11 



20 c. 400 to 300 3 



20 d. 500 to 400 130 



As they were almost absent from the Mesoplankton during 

 the 1896 cruise, I should not like to suggest, without more 

 extended observations, that the deeper specimens were at so great 

 a depth and so low a temperature, of their own free will. It 

 seems to me probable, although there was nothing in their 

 appearance either to suggest or to contradict it, that, in the haul 

 20 d, the net si ruck a swarm which had been killed by cold or 

 other unfavourable circumstances, and was slowly settling to the 

 bottom. The only differences between the specimens from 20 c 

 and 20 d, and those surface-specimens which were living when 

 brought on board, was that the digestive coil was blue in the 

 deep-water specimens, brown or reddish in the surface specimens. 

 Experiment would easily determine whether this was a post- 

 mortem change or not. 



1 " Such vast numbers with a very few exceptions of much the same 



size " (no Pflegethiere noticed) ; Herdman, op. cit. p. 111. " Erst bei genauerer 

 Durchsicht fand ich unter ihnen, wenn gleich in weitaus geringerer Zahl, 

 Pflegethiere und auch Ammen"; Borgert, op. cit. p. 61. " Ammen " were not 

 observed among the ' Research' specimens. 



2 Three were "Pflegethiere." 



