( c ) 



August I forced at 70°-8(T F. (21°-27° C.) a large number, 

 nearly 100, of larvre of A. levana, many not more than half 

 grown, the pupae being from pupation kept for months at about 

 70° F. (21° C.) and removed in batches at about fortnightly 

 intervals to 80°-90° F. (27°-32° C.) or a little higher ; not one 

 was converted by the process into the prorsa form, though one 

 was of the porima form ; all the rest died.* 



I am satisfied that to cause conversion in many cases the 

 temperature must be applied in a very early period in the 

 life of the individual. I have been trying experiments with 

 a view of ascertaining the exact period — varying doubtless 

 in many species — in which to be effective the change of 

 temperature ought to be administered, without having yet 

 attained sufficiently definite results to lay before the Society. 

 I am not sure that in some cases it would not be necessary 

 to make the application of temperature as far back as 

 the period when the egg is laid, and perhaps at a time when 

 it is still unlaid, so as to affect the "germ plasm" of the 

 parents or one of them. 



Races of Bombyx mori. 



The case of the common silkworm moth, Bombyx mori, a 

 species which hibernates in the egg, is interesting, as showing 

 how deeply ingrained the tendency to single-broodedness may 

 be as a hereditary character implanted in different races of a 

 single species. The race ordinarily cultivated in the south 

 temperate zone of the silk-producing countries of France, 

 Italy and Central Asia, and in Japan, has many varieties, 

 but (with the exception of a few bivoltine, trivoltine and even 

 quadrivoltine races locally cultivated in parts of Italy) their 

 cycle is annual. And yet there is a race usually cultivated in 

 Bengal which is polyvoltine, producing ten or eleven genera- 

 tions in a year. All the races interbreed freely. So essential 

 is a certain degree of cold to the univoltine race, that in order 

 that the eggs should hatch out healthily when transported to 

 the Punjab and Dehra Dun, which has been done to improve 



* Of 24 not thus forced as pupa; but kept out of doors 16 emerged in 

 the spring. 



