SECT. 2] AND WEIGHT 499 



development was that of Gaspard, who in 1822 constructed the fol- 

 lowing table : 



Developmental 



Temperature time of snail's 



(°C.) eggs in days 



6-8 45 



12 38 



20 21 



Gaspard also worked on frog's eggs. Davy and Coste, both in 1856, 

 published some figures showing the acceleration of development of 

 the eggs of the salmon in warmed water. Most of the early work 

 was, of course, fragmentary, and for various reasons unsatisfactory. 

 Thus Philipeaux in 1871 observed that the hatching time of axolotl 

 eggs was shortened from 25 to 8 days as warmth increased but he 

 did not take the temperatures, and Vernon stated in 1895 that the 

 optimum temperature for the development of the embryos of 

 echinoidea was from 7° to 22°, outside which limits they rapidly 

 became abnormal. Semper found that nauplii of Branchus and Apus 

 hatch out at a temperature of 30° in less than 24 hours, whereas at 

 16-20° they require some weeks. Again, lobster larvae reared at 

 23-27° passed the fourth moult in about 10 days, i.e. 3 days earlier 

 than larvae reared at 19° C., according to Herrick. Cuenot gave the 

 following figures for the hatching time of the locust : 



Table 68, partly from Davenport, shows the time taken in em- 

 bryonic development at various temperatures for certain fishes. 

 As we shall see further in the section on resistance and susceptibility, 

 there are to be found among embryos very obvious adaptations to 

 the environment in which they are to grow ; thus Rauber has shown 

 that the eggs of minnows and salmon which develop during the winter 

 will not grow at all at temperatures much above 12-15°, but will 

 do so at 0°. The critical points below and above which normal 

 development will not go on have been determined for amphibians 

 and birds by various observers, and are tabulated in Table 68. The 

 optimum temperature may be regarded as that at which the smallest 

 number of abnormal embryos are produced ; on each side of it the 

 amount of teratological effect will more or less rapidly increase, while 

 at the same time the rapidity of development will on the one hand 

 be increased and on the other hand be retarded. When a certain 



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