MORPHOLOGICAL ADAPTATION IN INSECTS — GRANDI 21 5 



previously examined Lepidoptera, though it functions in a like man- 

 ner. The thorax has very interesting features. Each of its three 

 segments has legs, which, however, are variously formed and lo- 

 calized. Indeed some legs (for instance in Fenusa iilmi Sund.) con- 

 sist of coxa, trochanter-femur, tibiotarsus, and a large claw, and 

 are little moved laterally outward; others (for instance in Fenella 

 nigrita Westw.) consist of the same but noticeably smaller parts 

 and are more displaced outward ; others, moreover ( for instance 

 in Phyllotoma accris McLachl. and P. microcephaJa Kl.), are reduced 

 to biarticulate, clawless stumps and are so much displaced outward as 

 to become nonfunctional at the sides of the segments. In all these 

 species, therefore, the thoracic legs have a tendency to be set toward 

 the sides of the somites and can reach their edges. Where their 

 natural seat was, two "ambulacral areas" have been formed as two 

 vicarious organs. Instead the abdominal legs have undergone an in- 

 volutive process and have been transformed into simple prominences 

 of little importance. The comparison between the behavior of the 

 Tenthredinidae mining larvae and that of the lepidopteran larvae 

 having similar habits is very interesting. We find the same tendency 

 in the modifications undergone by these insects, but in the former the 

 phenomenon is kept within more moderate limits ; this fact, neverthe- 

 less, has to be considered in relation also to their manifest plasticity 

 and to the fact that no known larva of a tenthredinid bores flattened 

 mines in only a single layer of cells of the leaf blade. Also in the 

 Tenthredinidae the thoracic and abdominal legs tend to undergo in- 

 volution and disappear, but here we are in the presence of a more or 

 less marked displacement with consequent uselessness of organs 

 (thoracic legs) and their replacement with new organs, probably 

 better fitted to cope with the resistance of the medium in which the 

 insect lives and feeds. No morphological "adaptation" can show bet- 

 ter than this does the course followed by it in its manifestations or 

 the ways of its determination and finally its biological meaning. 



V. LARVAE OF SOCIAL HYMENOPTERA APOCRITA 

 (VESPIDAE, APIDAE) 



It is well known that the larvae of the social Vespidae are nourished, 

 at least after a few days from their hatching, upon bits of crushed 

 insects brought to the nest by the nurses, which distribute and sub- 

 divide them among the progeny ; thus the larvae receive the pabulum 

 ventrally behind the head and may consume it at their ease by folding 

 their heads under the thorax. Equally well known is the extraordinary 



