l>r. II. M. 



and all <>f those heated to 40 J and 41 . After an hour, all of those 

 heated to 'M , ami half ot those heated to 10 . were free-swimming. 

 After four hours four-fifths of those heated to JU were freewimming, 

 luit none of those heated to 41 had recovered. The death temperature 

 w.-is therefore about 40'3\ 



These death temperature observations perhaps become more striking 

 if put in tabular form. Thus: 



It should l>e remarked that the embryos used in these ol>servation8 

 had been kept at 26 during development. Six days' plutei obtained 

 from the same stock of ova, but allowed to develop at 23 - 5 instead of 

 26, were found to have a death temperature of 39 -.3 \ Thus the 

 higher temperature of development had produced a certain amount of 

 acclimatisation. 



The bearing of these resxilts on the curious double effect of exposure 

 of the developing ova to high temperature is obvious. Thus, if a tem- 

 perature of 29 J is fatal to the vitality of ova at the time of impregna- 

 tion, the temperatures a few degrees below this are doubtless unfavour- 

 able to development. Still lower temperatures, on the other hand, are 

 known to exert a favourable influence. Now as in the course of 

 development the death temperature gradually rises, one is quite 

 justified in concluding that the lower limit of the unfavourable tem- 

 perature rises too, and very probably to a more or less similar extent. 

 In the above experiments it was found that up to the end of four hours 

 a temperature of 26 J was distinctly unfavourable to growth. During 

 the next four hours it was more or less neutral, but after this time it 

 was most distinctly favourable. Now the present observations show 

 that between the 4th and 12th hours the death temperature rises about 

 3, so what was an 'unfavourable temperature to the earlier stage of 

 development may have become converted into a favourable one to the 

 later stage. 



Let us now return to the results on the effects of temporary subjection 

 to abnormal temperatures. These were obtained under such a variety 

 of conditions that one is scarcely warranted in grouping them all 

 together, but the majority of them can be split up into three more or 

 less homogeneous groups. In one the so-called normal larvae were 



