24, MEMOIKS OK THE NATIONAL ACADEMY OF SCIENCES. 



and the above-iiicntioiieil group, I'licosia, Lei()C:irii])a) should properly, by their smooth, iioctui- 

 form shape, stand at the bottom of the family, as beiuff nearest related to the primitive form of the 

 group. lUit until we know more of the earliest stages it is best to suspend our Judgment. 



1. The moi-e jtrominent tubercles and sjiines or bristles arising from them are hypertr<iiiliie<l 

 piliferous warts, the wart.s with the seta or hair whieli they bear being eoinmon to all caterpillars. 



2. The hypertrophy or enlargement was probably primarily due to a change of station from 

 herbs to trees, involving better air, a more etjuable temperature, perliaps a diHereiit and better 

 food. 



3. The enliirged and specialized tubercles developed more rapidly on certain segments than 

 others, especially the more prominent segments, because the nnrritive Huids would tend to more 

 freely supply parts most exposed to exteriml 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 adaptation to tree lile. 



5. As the result of some unknown factor several of the hypodermic cells at the Ijasc of the 

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



0. After such primitive forms, members of different families, jiad become established on trees, 

 a process of arboreal segregation or isolation -would set in, and intercrossing with low feeders 

 would cease. 



7. Heredity, or the unknown factors of which heredity is the result, would go on uninter- 

 ruptedly, the result being a succession of generations perfectly adapted to arboreal life. 



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

 toward the elaboration and preservation of the new varieties, species, and genera, and would not 

 cease to act in a given direction so long as tbe 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 tbe origination of variations, were in the beginning due to the primary 

 (direct aiul iiulirect) factoi'S of evolution (Neolamarckism), and the final stages were due to the 

 secondary factors, segregation and natural selection (Darwinism). 



III.— OX CERTAIN POINTS IN THE EXTERNAL ANATOMY OF BOMBYCINE LARV.€. 



Homology of the '■'■Jiayellum'^ of Centra, ete., with the planta of the other tibdomiital let/.s. — We 

 have in a former ' article, in describing the lai'vsB of Macrtirocampa marthesia and of certain species of 

 Cerura, called attention to the nnXure of the stenuipoda- or filamental legs of those caterpillars, 

 and their generally undisputed homology witli tlie anal legs of other Notodontians. I'l. XXXVII, 

 fig. 9, represents the anal legs of Daniilophia anguinn in its first larval stage. It is internuHliate in 

 form between the normal leg and the stemapod. It has no crochets, but the planta, of whicli the 

 "flagellum" of Cerura and H. marthesia seems to be the homologue, is retracted and the retractor 

 nius(^les, one of which is divided, are much as in the filaniental legs of Cerura, etc. 



Note on the modifications in the tenant or (/landidar hairs of the thoracic feet. — As is well known, 

 the thora(;ic feet of caterpillars are five Jointed and end in a single claw, with apparently a 

 rudimentaiy one at the base. Usually, besides the unguis or claw, there is a tenant hair, which 

 is generally spine like, but besides these appendages there are sometimes more or less flattenecl, 

 lamellate seta;, which are curious and worthy of notice. In Parorgyia paraUela, besides the unguis 



' Proceedings Boston Soc. Nat. Hist., xxiv, 1890. 



^Tho term "tails" or p;iii(lal filaments is too vague for these highly modified anal legs; hence we jirnpose the 

 term etimapoda or stemapods for those of Cernra and Macrurocam])a. The diTivatioii is Gr. ani/ui, lihiment, Troij-, 

 TTorW, leg or foot. Mr. J. Ilellins, referring to these organs in liucklcr's Larvir of tlie liritisli liutterllics and 

 Moths (Ho.v. Soc., ii, 13H), remarks: "Hut now through Dr. T. A. t'liapmau's good tcacliing, I regard them as dorsal 

 appendages, somewliat after the fashion of the anal sjiines of thi; larvie of tlie Satyrid.r.'' Tliis, I am satistiud, is au 

 error. After repeated comparisons of the tilatneutal anal legs of Cerura with tluise of Mdcriirocanipa marthinUi, and 

 comparing these with tlio greatly elongated anal legs of young //. iniirolor as figureil l>y I'openoe, and taking into 

 account the structures and homologies of the snpraaual and paranal ilap.s, one can scarcely doubt that those of 

 Cerura are modified anal legs. 



