491 



food or not. Tn some species the factors of the sensory stim- 

 ulns are so nnmerons or so particular that the species will 

 react only nnder very narrow limits while in others the range 

 of reaction is much broader and in such species we find these 

 "lapses of instinct" occurring. These are the species in which 

 we find considerable adaptability of habits and the wide range 

 of reaction is of value to the species since the eggs laid almost 

 at random serve to find for the species additional sources of 

 food which would be missed by a species reacting within nar- 

 rower limits. 



The adaptability so secured may, as has been shown by 

 Cushman, serve to carry over a species on uinusual food when 

 its preferred food-plant for any reason fails to seed. This 

 adaptability may also serve to permit wider dispersal of the 

 species. Thus the adaptability of the Bruchus pruininus per- 

 mitted it to shift to Leucaena glauca from Acacia after having 

 shifted from Olneya tesota to the Acacia, and it has been able 

 to establish itself in the Islands while the more narrowly re- 

 acting Bruchus pisoruni appears as yet to have failed. 



One of the curious things in experimental work with Bru- 

 chidae is that very often, as shown by breedings made under 

 natural conditions, a species will not naturally breed in certain 

 host plants but when confined with the seeds will oviposit and 

 develop in them. From this it seems to me we must distin- 

 guish between the sensory stimuli which cause the Bruchus 

 to approach and alight upon the larval food and the oviposition 

 stimuli proper. The visual faculties of the insects appear to be 

 most prominent in the former, at any rate I have seen what 

 were apparently attempts of a Bruchus to settle on seeds with- 

 in a glass tube and resting on the glass over them wdien actual 

 contact was impossible. In the oviposition reflexes tactile 

 stimuli through the antennae and perhaps the tarsi must play 

 an important part. 



In some cases it is possible to analyse the complex reflex 

 of oviposition with interesting results. Mr. Timberlake has 

 been able to show that there is an olfactory element in the 



