112 Zoologica: N. Y. Zoological Society [HI; 3 



dubious in regard to the whole subject of the tropisms. My 

 present position concerning them is not essentially different 

 from that of Jennings (1904, 1906, 1909), von Buddenbrock 

 (1915), Claparede (1912, 1913), and others. I should, therefore, 

 interpret them as adaptive, secondarily developed reflexes and 

 not as unique, primitive elements in the genesis of instinctive 

 behavior. 



There are, nevertheless, in the behavior of Coccidotrophus 

 certain phenomena, which some might be inclined to interpret 

 as tropisms, especially the reactions to contact, light and chemical 

 stimuli. The reader wha has followed my account of the beetle 

 will have noticed the peculiar orientation of some of its stages 

 and of some of the associated insects with respect to the walls 

 of the long fusiform petiolar cavity which they inhabit. Thus 

 the eggs, cocoons and pupse of the beetle are always placed with 

 their long axes parallel with the long axis of the petiole, and 

 the coccids, while feeding, the cocoons of Blepyrus, which are 

 formed within the bodies of the coccids, and the nude pupse of 

 Scymnus assume the same orientation. The food grooves which 

 are excavated by the beetles and the frass-ridges which they 

 build, as well as the longer axis of the entrance are all longitu- 

 dinal. Moreover, the beetles spend much time lying in the food- 

 grooves with their narrow bodies longitudinally oriented and 

 with as much as possible of their surface in contact with the 

 floor and walls of the grooves. 



At first sight this striking series of orientations would seem 

 to be best described as tropistic, perhaps as due to some form 

 of thigmotropism, but it is evident that the only behavior which 

 might be legitimately regarded as such is that of the adult beetle 

 when resting or moving in the food grooves. The Collembolans 

 and the larvae of Scymnus and Diadiplosis exhibit not the slightest 

 tendency to assume a similar orientation, and the Coccidotrophus 

 larvae show no traces of it till they start their cocoons. Even 

 then, though they orient their cocoons, they assume a position 

 with their long axes parallel with the long axis of the petiole 

 only while actually adding particles to the walls and after they 

 have pupated. It is evident, furthermore, that nearly all the 

 orientations mentioned can be traced more or less directly to 

 peculiarities in the structure of the petiole, i.e., to the shape of 



