

Dr. H. M. Y 



Still. a^ain, it was thought that the vigorous .^tin-ing of the water 

 wliich w.i- necessary in order to distribute the organisms evenly 

 through it previous to withdrawal of a portion, might perhaps exert a 

 retarding influence on development. However, this was evidently not 

 so, as, in two experiments, in which the wat-r \va- absolutely unstirred 

 throughout, the resulting larvae varied by respectively + 2*0 and - 2-& 

 per cent, from those derived from frequently-stirred water. 



In the last experiment to lx> described the developing ova were kept 

 at 25 and not at 26. Consequently, the diminution produced in the 

 size is not so great. In this case, also, two parallel series of observa- 

 tions were made, one with Strongyloccntrt>tn.< ova as usual, and another 

 with the ova of Sphwrechinus granulari*. In the former case, the- 

 unfavourable effect of the high temperature persisted till the end of the 



9th hour, and, in the latter, until at least the 21st hour, and possibly 

 even later. The Sphwcchmus ova did not react so much to the environ- 

 ment as the Stronyylocenirotu-s, just as was found to be the case in the 

 experiments on the effect of temperature at the time of impregnation. 

 Still these observations on Spha-rerhiwis, as far as they go, more or less 

 support the conclusion drawn from the ArVMgjfiMmJrisfM experiments, 

 viz., that there is a diminishing reaction to environment as the stages of 

 development progress. 



We see, then, that in all of these four sets of olservations the 

 originally unfavourable influence of the high temperature is later on 

 converted into a favourable one. What is the cause of this 1 No- 

 absolute explanation was arrived at, but some observations made on 

 the maximum or death temperatures of the developing ova gave a very 

 satisfactory partial explanation. In these observations portions of 

 the water containing the ova in various stages of development were 

 placed in a beaker, and this was placed in a larger l>eaker of water 

 which was gradually warmed. The beaker containing the ova was 

 continuoiiftly stirred with a thermometer, and when the required tern- 



