309 



Evolution of Bristles, Spines, and Tubercles with caterpillars.* — Papers of 

 this character always interest the working entomologist. Dr. Packard, 

 from his broad knowledge of forms, is well qualified to generalize, as 

 he has done in this instance. His paper is confessedly suggested by 

 the "epoch-making work of Weissman" and by the more recent papers 

 of Meldola and Poulton. His thesis is announced in the full title given 

 in our foot-note, and he brings a vast number of observations to bear 

 in its support. He discusses not only the bristles, spines, and tuber- 

 cles, but also the colorational markings, and incidentally introduces 

 more or less complete descriptions of eighteen Notodontid larvse, and 

 adds a grouping of these larvae according to their aftiuities and also 

 according to their adaptation to arboreal life. The subject is largely 

 speculative, and we give Dr. Packard's conclusions in brief. 



1. The more prominent tubercles, and spines or bristles arising from them, are hy- 

 pertrophied piliferous warts, the warts with the seta or hair which they bear being 

 common to all caterpillars. 



2. The hypertrophy or enlargement was probably primarily due to a change of sta- 

 tion from herbs to trees, involving better air, a more equable temperature, perhaps a 

 different and better food. 



3. The enlarged and specialized tubercles develope more rapidly on certain seg- 

 ments than others, especially the more prominent segments, because the nutritive 

 fluids would tend to more freely supply parts most exposed to external stimuli, 



4. The stimuli were in great part due to the visits of insects and birds, resulting 

 in a mimicry of the spines and projections on the trees ; the colors (lines and spots) 

 were due to light or shade, with the general result of protective mimicry or adapta- 

 tion to tree life. 



5. As the result ot some unknown factor some of the nypodermic cells at the base 

 of the spines became in certain forms specialized so as to secrete a poisonous fluid. 



6. After such primitive forms, members of different families, had become established 

 on trees, a process of arboreal segregation or isolation would set in, and intercross- 

 ing with low feeders would cease. 



7. Heredity, or the unknown factors of which heredity is the result, w^ould go on 

 uninterruptedly ; the result being a succession of generations perfectly adapted to 

 arboreal life. 



8. Finally the conservative agency of natural selection would operate, constantly 

 tending towards the preservation of the new varieties, species, and genera, and would 

 not cease to act, in a given direction, so long as the environment remained the same. 



9. Thus in order to account for the origin of a species, genus, family, order, or even 

 a class, the first steps causing the origination of variations were in the beginning due 

 to the primary (direct and indirect) factors of evolution (Neolamarckism), and the 

 final stages were due to the secondary factors, segregation and natural selection 

 (Darwinism), 



*Notes on the evolution of bristles, spines, and tubercles of certain caterpillars, 

 apparently resulting from a change from low feeding to arboreal habits; illustrated 

 by the life- histories of certain notodontians. By Alpheus S. Packard, Extracted 

 from the Proceedings of the Boston Society of Natural History, Vol. xxiv, 18'J0, 

 pp. 493-560. Plates ill and iv. 



