H'2 Mr. Merri field's incident. il olif^rrrationfi 



high temperature, m others most reluctantly ; how far 

 the temperature affects the size, shape, markings, and 

 colouring of the perfect insect, and in what particular 

 period of development the change is caused. The 

 well-known work of Prof. Weismann, as translated and 

 annotated by Prof. Meldola, throws the greatest light on 

 these questions, but cannot in the nature of things 

 exhaust so large a subject. So far as my experiments 

 on pupffi have gone, the results of them appear in close 

 accordance with those of Prof. Weismann, but other 

 experiments seem to indicate that the temperature to 

 which the larva is exposed in its growing stages has 

 much to do with the colouring of the perfect insect. 

 Difference of size, — a kind of difference associated with 

 seasonal dimorphism, may be supposed to depend on 

 the conditions to which the larva in its growing stages 

 is exposed, rather than on those to which the pupa is sub- 

 jected. 1 think this difference of size in the selenias 

 experimented on, as between the summer and spring 

 emergences, not overstated at three to four as tested by 

 weight, and five to six as tested by wing-expansion ; but 

 these proportions are by no means constant ; and, besides 

 the considerable difference in size between individuals of 

 the same brood, there are also great differences between 

 the same emergence, {i.e., spring or summer) in different 

 years. 



I will first mention such results obtained as bear on 

 the subject of size. It will be observed, on referring to 

 the table given in my paper of last December, that the 

 broods of illunaria forced at a temperature of 75° to 

 80° or upwards, increased in size from the " second " 

 generation (first summer emergence) to the " third," 

 and from the "third" to the "fourth" (they fell off 

 in the next unhealthy generation) ; also, that of the 

 three sets of the "second" generation, the sleeved 

 were the smallest, the forced considerably larger, and 

 the "bottled" somewhat larger still ; i.e., those which 

 had been bred at an ordinary temperature were con- 

 siderably smaller than the others, and of those others, 

 such as had the higher temperature were slightly the 

 smaller. 1887 was a very fine, dry, sunshiny summer inthe 

 south of England, and June and July were rather above 

 the average in temperature, though all the other months 

 were somewhat below. The sunnner of 1888 will be 



