1913.] 9 



I arrived at this coiiclusiou first by the uon-winter apterous 

 moths, which Mr. Hudson leaves ou one side. Of these, those I had 

 studied for other reasons, Psychids (macro and micro) Orgyias, 

 Heterogynids, &c., all lay their eggs on or in their cocoons or pupa- 

 shells (and certain Arctiids are approximating to this position) . For 

 these the possession of wings would be an obvious danger. 



For the winter moths, Mr. Hudson agrees with me that separation 

 from the neighbourhood of the food-plant is the danger to be escaped. 

 He considers that a winged moth might he too much numbed by cold 

 and unable to return if it flew away from the food-plant. Such a 

 danger no doubt exists to an appreciable extent, but it is obvious that 

 if a moth was too much numbed to return to the food- plant it would 

 be also too lethargic to lay any eggs if it had remained there. Yet we 

 do not find the eggs of these moths laid anywhere, as by incapacitated 

 individuals, but always in places duly selected. 



The point on which Mr. Hudson's explanation differs from mine 

 is precisely here. I do not think cold jje;v se has any appreciable 

 effect, but that the dominating cause that would prevent the insect 

 from finding the original or some other food-plant, is not, were it able 

 to fly, a secondary inability due to cold, but a primary one, that with 

 full powers of flight it could not find the food-plant. Nocturnal Lejji- 

 doptera on the wing, no doubt discover the food-plant by scent. When 

 vegetation is dormant in winter the scent will be trifling, for a moth 

 on the wing, practically non-existent. Therefore, a moth once taking 

 a flight will not again find the food-plant. There is probably, how- 

 ever, enough scent or other suflicient indication to be detected by the 

 moth when at the close quarters demanded by travel on foot. 



Mr. Hudson is also on sure ground when he says that these 

 species affect plants that are more or less gregarious in hedges 

 and thickets. 



It may be noted that some of the commonest of these insects, 

 0. hrwmata, G. fagella, &c., have larvae that live spun up, and that 

 the dissemination of the species in these cases must be by the 

 wandering of these apterous females. In the other large section, of 

 summer species, whose eggs are laid on or in the cocoon, the wander- 

 ings of the larvae must be the means of extending their habitats. 



It is perhaps desirable to note, in reference to one remark of 

 Mr. Hudson's, that there is a general agreement that 0. afitiqiia in 

 England has only one brood in the year, but that there is a great 

 range in the periods of the eggs hatching, even of one batch, and 



