1871.) 123 
It is the purpose of the present communication to point out the 
probable universality of this law—that caterpillars of butterflies 
present greater structural differences between the embryonic and adult 
stages of the same individual, than are to be found in the adult larve 
of allied genera. By the term “embryonic,” I designate those cater- 
pillars which have not changed their condition since leaving the egg, a 
stage in which they generally continue but one or two days. Some of 
the changes alluded to are more or less gradual in their appearance, 
but they generally occur at the first moulting of the caterpillar. 
| All the instances given are drawn from New England butterflies, 
and the generic terms employed are those used in my list, published in 
the Proceedings of the Boston Society of Natural History. If any one 
is sceptical in regard to the facts adduced, I can enter more into detail 
upon doubtful points. It should also be premised, that in studying 
caterpillars, the shape and sculpturing of the head, the form of certain 
segments, and especially the precise number, location and disposition 
of the spines, thorns, and hair-emitting warts of the body, will be 
found to furnish abundant means of distinguishing the most closely 
allied and minutely sub-divided genera. But to our examples. 
In the genus Satyrus, the body of the young larva is furnished with 
exceedingly long, scarcely tapering, compressed hairs, geniculate a little 
beyond the base, serrulate above, and generally directed backwards ; 
those, however, which occur on the upper portion of the thoracic seg- 
‘ments are directed forward, and thus present a very peculiar contrast. 
‘Nothing of this sort appears on the mature larva, which is represented 
‘by Boisduval and Le Conte as quite smooth, but which is probably 
uniformly clothed with very short hairs. 
In the genus Hipparchia, the young larva is born with a head of 
equal height and breadth, furnished with prominent lateral and frontal 
‘warts. The body has four pairs of longitudinal rows of tubercles de- 
finitely disposed, each tubercle bearing a short, straight, delicately 
‘clubbed bristle. The head of the mature larva, on the other hand, 
‘bears no lateral or frontal warts, but either half is prolonged upwards 
‘into a conical horn as long as the head itself; while the body is fur- 
nished only with microscopic hairs, irregularly distributed. In both 
this and Satyrus the bifurcation of the last segment of the mature 
larva, long known as a characteristic of the sub-family of Satyrine, is 
scarcely perceptible in the embryonic caterpillar, being indicated in 
Satyrus only by slight tubercles. 
In Limenitis, the head of the young larva is smooth and equal, and 
the body uniform in size throughout, studded with numerous equal, 
