746 LT.-COL. N. MANDERS ON THE 



Instances of Imitation by Young Crows. 



July, 1910. I saw an old ciow and two young ones on the Rifle 

 Green this morning ; one of the youngsters had hold of a bone 

 with a piece of gristle attached to it. It was so firmly adhei-ent 

 that the bird could not detach it as the bone constantly moved 

 with the bird's efforts, and eventually it gave up. Then the old 

 bird, which had been standing by all the time, went to the bone, 

 put its foot on it, thereby gaining a purchase, and tore ofi" the 

 gristle without difficulty ; the young bird after two or three 

 attempts did the same. 



September, 1910. An old crow had a piece of hard boiled 

 potato ofi" which it was picking pieces and giving them to a 

 full-fledged young one close by. A goodly number of detached 

 pieces lay on the ground and attracted the attention of some 

 other crows, which flew down and began picking them up ; seeing 

 this the youngster did likewise, though it made no attempt to do 

 so before their arrival. 



Seasonal Dimorphism — Cryptic Defence. 



I should not conclude this study of mimicry without discussing 

 that form of it which is known as " cryptic defence," and especi- 

 ally that which is so noticeable in the seasonal changes of so 

 many tropical butterflies. 



It is commonly believed to have been produced by natural 

 selection acting through the medium of insectivorous foes, the 

 more exact and perfect imitations found in the dry season being 

 due to the paucity of insect life at that time of the year, which 

 produces a greater keenness in pursuit and a greater struggle for 

 existence. The argument has been put forward in full by 

 Professor Poulton in his ' Essays on Evolution,' page 203. 



I hope in the near future to deal more exhaustively with this 

 subject, but at present will only direct attention to two species 

 occurring in these islands, a study of which does not favour the 

 usually accepted views. The contention for the production of the 

 dry season form rests upon the premiss that " the dry season is a 

 time of far greater pressure than the wet " ; for although the 

 enemies of insects are fewer, the insects themselves are pro- 

 portionately even more reduced, and "the light thrown by recent 

 investigation leads us confidently to believe that the differences 

 between the seasonal forms — hitherto devoid of interpretation — 

 have a meaning and a value in the struggle for existence and 

 came into being under the sway of natural selection " [Poulton). 



Thou oh it is probably correct to say that in countries such as 

 S. Africa and India, which have a continental climate, the seasons 

 are such as to produce a wealth or poverty of insect life, it is de- 

 cidedly incorrect to assume the same with regard to the islands 

 we have been investigating. There is no doubt that at no season 

 of the year is thei-e in any of them a paucity of insect life, and at 



