24 
MEMOIKS OF THE ^"ATIONAL ACADE3IY OF SCIENCES. 
and tlie above-iiieutioned group, Pheosia, Leiocuinpa) sliould propci-ly, by tlieir smooth, iioctui- 
form shape, stand at the bottom of the family, as being nearest related to the primitive form of the 
group. But until we know more of the earliest stages it is best to suspend our judgment. 
1. The more prominent tubercles and sjnnes or bristles arising from them are hy])ertroi)hied 
piliferous warts, the warts with the seta or hair which they bear being common to all caterpillars. 
2. The hypertrophy or enlargement was probably ])rimarily due to a change of station from 
herbs to trees, involving better air, a more equable temperature, perhaps a different and better 
food. 
3. Tlie enlarged and specialized tubercles developed more rai)idly on certain segments than 
others, especially the more prominent segments, because the nutritive fluids would tend to more 
freely supply parts most exposed to external stimuli. 
d. The stimuli were in great part due to the visits of insects and birds, residting 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 life. 
5. As the result of some unknown factor several of the hypodermic cells at the base of the 
spines became in certain forms specialized so as to secrete a poisonous fluid. 
0. After such primitive forms, members of different families, had 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 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 (ISTeolamarckism), and the final stages were due to the 
secondary factors, segregation and natural selection (Darwinism). 
III.— OX CEKTAIX POINTS IN THE EXTERNAL ANATOMY OF BOMBYCINE LARV.-E. 
Homology of the ^^ilagellum"'* of Centra j etc,^ icith the jylania of the other <ih(lominal legs. — We 
have iu a former * article, in describing the laiwm of Macritrocampa mariheski and of certain si^ecies of 
Oeinira, called attention to the nature of the stemapoda‘^ or filameutal legs of those caterpillars, 
and their generally undisputed homology with the anal legs of other Yotodontians. PI. XXXA^II, 
fig. 9, represents the anal legs of Dasylophia angaina in its first larvnd stage. It is intermediate in 
form between the normal leg and the stemapod. It has no crochets, but the plauta, of which the 
“flagellum’- of Cerura and H, marihesia seems to be the homologue, is retracted and the retractor 
muscles, one of which is divdded, are much as iu the filameutal legs of Cerura, etc. 
Hole on the modifications in the tenan t or glandular hairs of the thoracic feet. — As is well known, 
the thoracic feet of caterpillars are five jointed and end in a single claw, with apparently a 
rudimentary 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 flattened, 
lamellate setae, which are curious and woythy of notice. In Farorgyia jtarallela, besides the ungmis 
^Proceedings Boston Soc. Nat. Hist.,xxiv, 1890. 
2Tlio term or caudal lilaments is too vague for these highly modified anal legs; hence we propose the 
term ateinapoda or steraapods for those of Cerura and Macrurocampa. The derivatiou.is Gr. filament, Troir, 
noMCf leg or foot. Mr. J. Helllns, referring to those organs in Buckler's Larvm of the British Butterflies and 
Moths (Roy. Soc., ii, 338), remarks: “But now through Dr. T. A. Chapman's good teaching, I regard them as dorsal 
appendages, somewhat after the fashion of the anal spines of the larvio of the Satyridie.” This, 1 am satisfied, is an 
error. After repeated comparisons of the filameutal anal legs of Cerura with those of Mavrni'ocanipa marihesia^ and 
comparing these with the greatly elongated anal legs of young H. unicolor as figured by Popeuoe, and taking into 
account the structures and homologies of the supraaiial and paraual flai)s, one can scarcely doubt that those of 
Cerura are modified anal legs. 
