I'll 



I>r. 11. M. V.-nion. 



(uantities of hot or cold water couM In- added t> l>rin- tin- temperature 

 . tly what was required. The room in whieh this tank was kept 

 was shut up closely at night so as to prevent cooling. 



In the first experiment some of the ova, after an hour's impregnation 

 at -'2 - , were kept for varying periods in this tank of water at 26'0 J , 

 and portions of them transferred in smaller jars to Aquarium tank 

 water at a mean temperature of 2.'i-.~> . The following results were 

 obtained : 



Here we see that three hours' exposure of the developing ova to a 

 temperature of 26 produced a diminution of 11 '7 per cent, in the size 

 of the larvae. Further exposure, on the other hand, not only failed to 

 produce a further diminution of size, but gave an actual increase, which 

 gradually became more and more marked. It is obvious, therefore, that 

 a temperature of 26, though harmful to the ova in their earlier stages 

 of development, becomes advantageous in the later stages. The reason 

 of this will be made evident further on. It might be thought at first 

 sight that this and other similar experiments in which the environment 

 produces a varying effect, could be of no use in deciding the question 

 under discussion. By judicious selection of certain of the values, how- 

 ever, useful results are obtainable. Thus, in the present instance, we 

 see that by the end of the 8th hour the favourable action of the high 

 temperature has already established itself, and it remains established 

 from that time onwards. All results obtained after this period are, 

 therefore, of value, and the figures which show that the effect produced 

 between the 8th and 12th hours is three times as great as that between 

 the llth and 22nd hours, are genuine ones. The apparent slight 

 diminution of size occurring between the 22nd and 144th hours is doubt- 

 less due to experimental error. In all the observations made during 

 the summer months the larvae were killed and preserved after only six 

 days' growth, instead of eight. This was because they practically reach 

 their maximum size in this period, the rate of growth being so much 

 greater than at the lower temperatures experienced in the spring. 



In the next experiment, the adverse effect produced during the first 

 few hours' exposure was extraordinarily urcat. so that the favourable 





