1894. FURTHER NOTES ON INSECTS. 367 



which, a few days later, it emerges, and passes the rest of its life, 

 which lasts several weeks more, feeding freely upon the leaves of the 

 tree. This is an observation of much interest, giving us a link 

 between the habits of grubs like those of N. salicis, L., which feed 

 openly all their lives, and those like N. salicis-cinevecs and N . gallicola, 

 which do not come out of their galls till nearly ready to pupate. The 

 pupal stage of the present species is passed in a cocoon buried in the 

 ground. The brood of flies, consisting entirely of females, appears in 

 August, and a parthenogenetic egg-laying ensues. The grubs of this 

 second generation pass through a similar experience to those of the 

 summer brood, and are full-fed by the time the leaves of their food- 

 tree are ready to fall. The winter is passed by the insects underground 

 as pupae, and among the flies produced from these in the following 

 spring a few males are found. Thus, as in so many other cases 

 among insects, sexual and virgin reproduction alternate. 



Dr. Heim concludes his memoir with some general considerations 

 on galls, in which, as already mentioned, he defends the view that 

 those structures are due to the action of poison injected by the parent 

 insect. He compares the dense parenchyma of the gall of Nematus 

 with the cell-proliferation which occurs in cancerous tissues in man, 

 criticises M. Beyetinck's comparison of the structure of galls to that 

 of shoots, and calls attention to the analogy between galls and fruits, 

 suggesting that the action of the insect-poison on the leaf-tissues is 

 comparable to that of a secretion of the pollen-tube upon the carpels 

 of a fertilised flower. 



Though the hymenoptera surpass all other insects in the interest 

 of their habits, much is to be learnt from the other orders. Dr. A. 

 Seitz has recently (5) collected a large number of noteworthy facts 

 regarding the butterflies and moths, with special reference to their 

 feeding in the larval and perfect stages. The first meal of a young 

 caterpillar is well-known to be often its empty egg-shell ; from this it 

 turns to feed upon the leaves whereon its provident parent had laid 

 her eggs. But in a few cases hatching takes place in winter or 

 early spring, and the young larvae have then to find a temporary food 

 until their own special plant is available. For example, the cater- 

 pillars of some species of Xanthia and other noctuid moths feed at 

 first upon willow-catkins. All who have tried to rear caterpillars 

 know that, while those of some species will feed only on one particular 

 species of plant, others will eat several species of the same genus or 

 family, while others again are still less particular, some being able to 

 feed on almost any green herb. That caterpillars, in this respect, 

 have often very nice tastes there can be no doubt, and Dr. Seitz 

 suggests further that the jaws of certain species are unable to bite 

 leaves of different textures. It is curious to note how certain species 

 change their food in different localities, a caterpillar confined to one 

 plant in one place being less particular elsewhere. Individual 

 aberrations in food are of special interest, in suggesting the starting 



