MELANISM AND MELANOCHROISM. 231 



Merrifield then goes into particulars of these two broods, 

 together with the third or " bottled " brood. But, in all these 

 particulars Mr. Merrifield argues as if only temperature were to 

 be noticed, although he states that whilst there was so much 

 difference between the " forced " and " sleeved " imagines, the 

 " bottled," kept indoors at a comparatively high temperature, 

 and which, if temperature were the prevailing factor, ought to 

 be more like the " forced," turned out to be, " in colour and 

 intensity of marking, not far from the sleeved." The process 

 of " bottling " at once tends to place the larva; under moist 

 and humid conditions, which seem to have affected these in the 

 same way as the rain of 1888 affected the sleeved. Mr. 

 Merrifield then writes : — " If the great difference between the 

 forced and the sleeved originated in the pupal period, it would 

 seem to follow, that the difference between about 66° and about 

 75°-8o°, during an exposure of a very few weeks, is sufficient, 

 in this species for the purpose " (p. 8g). Now, I would ask, 

 how, in the name of common-sense could this be ? If this 

 were so, pupae subjected to this difference of temperature would 

 produce two forms of the same moth, and every mitiimnaria 

 spending its pupal period at 66° should have a tendency to 

 melanism. Other species, I presume, should follow the same 

 rule. Nothing, I think, better shows that Mr. Merrifield was 

 right, when he wrote : — " I think the larval period is the 

 critical one," and again :— " I do not think temperature can 

 ever convert one form into the other, unless brought to bear on 

 the larval stage," than the extract just quoted. There is no 

 doubt the action of moisture (it may be more or less affected 

 by temperature at the same time, but I fail to see how) on 

 the larva is the cause of the darkening. 



Professor Weismann had recourse to a very far-fetched 

 notion to explain the reason why he supposed, that, although 

 a difference of 14.9'^ R. (33-5° F.) between the German winter 

 and summer temperatures failed to originate a climatic 

 variety of Papilio podalirius, a difference of 9° F. between the 

 summer temperatures of Germany and Sicily was sufficient to 

 do so ; his suggestion being, that the cause was to be found in 

 the absolute temperature reached ; and I am rather surprised 

 that Mr. Merrifield seems inclined to follow him in (what 

 appears to me) his fallacious reasoning. However, for our 

 purpose, it is sufficient to consider that Professor Weismann 

 and Mr. Merrifield are both obliged to leave the " cold " theory, 

 to explain in other ways, why climatic races are developed in 



