MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 
27 
grooves passing down tlie shaft from tlie notches between the teetli. They occur not only on the 
back and sides of the body segments, but also on the sides of the abdominal legs. The occurrence 
of such hairs in this genus is interesting from the fact that they have not yet been observed in 
Arctiaus, to which this moth has been referred, nor in the Xoctuidie, among which it should be 
placed, since no Arctiaus have when hatched smooth glandular hairs. ^ 
IV.— ON THE IXCONTiRUENCE BETWEEN THE LARVAL AND ADULT CHARACTERS OF NOTODONTIANS. 
As is well known to zoologists, Rom the writings of Fiitz Miiller and later students, in groups 
of animals which generally undergo a metamorphosis, two or more species of the same genus may 
diner remarkably in respect to their early life, one species passing tiu’ough a complicated meta- 
morphosis while a closely allied form has a direct development, hatching in the form of the adult, 
The embryo, however, in the latter case rapidly passes through a series of changes, constituting 
a premature, abbreviated, or condensed metamorphosis, epitomizing the ordinary early stage of its 
metamorphic allies. Thus the lobster differs from the other marine macruran Crustacea in having a 
condensed metamorphosis before hatching from the egg, rapidly passing through anau])lius and 
a zoi‘a phase. It is so with some crabs. All the fresh- water Decapoda, notably the crayfish, have 
no postembryonic metamorphosis. The fact that the embryo exhibits a condensed metamorphosis 
shows tlieir origin from metamorphic forms. 
These are perhaps the most remarkable eases of incongruence between what may be closely 
allied genera and even species. 
Also two allied species of Gamiuarus may differ in toto as regards the mode of segmentation 
of the yolk, total cleavage occurring in one marine species {G, locnsta) and partial or peripheral 
cleavage in two fresh-water forms (fr. and fluviatilis). 
Examples of such great divergences in larval or early life, or in the condition in which the 
animal is hatched, in sx)ecics closely similar in adult life, are not uncommon in worms, Echiiioderms, 
Molluscs, Crustacea, besides insects, and the plieuomenou is with little doubt due to the changed 
conditions of the e!ivironments to which forms with such exceptional modes of development have 
been exposed. 
The principle, Then, of divergence or incongrnence of larval characters in forms Avhose adults 
are closely allied has been established in tlie lower classes of Nletazoa. The most remarkable 
alid ))uzzling case, x>erhaps, is that of Ilalanoglossus, whose Tornaria larva is so much like that of 
Echiiioderms, while the adult is a protoehordate animal. 
As a matter of fact this does not affect the classification of these animals. Zoologists liave 
not thrown forms with a direct development into distinct groups where the adults have not 
shown any diflerences; at the same time no one wouhl unite the two species recognized as such 
which presented no easily observed differences if one had a direct and the other a metamorphic 
development. In the present state of our knowledge it may be well to at least provisionally 
mark tbe difiereuces between the two forms, so div^ergent in their early life, by giving them 
distinct names, and thus emphasizing the fact that of the two closely allied forms one has 
diverged from the other through having been subjected to a different set of external iufiucnces, 
whatever such conditions may have been. 
Systematic zoology has undergone within the last thirty years an entire change. Our present 
systems of classification are now attempts to arrange animals in the order of their probable 
apjoearance, i. e., phylogeuetically, and as the subject is yet in its infancy, and our attempts 
provisioual and tentative, we are obliged to give great weight to any differences in the larval 
conditions of animals with a metamorphosis, because such differences were undoubteiily due to 
differences in tlie environments of their i>arents. Indeed if it had not been owing to changes in 
the i^hysical and biological emuronment, animals would never have risen beyond the dead level 
of the lowest Protozoa. 
Such reflections as these and a knowledge of the mode of deyelox)ment of the lower classes 
of invertebrates are all-iinx)ortant to the students of insects, esi)ecially of the metamorphic orders, 
•n. XXXVII, fig. 12. Glandular liaiis of Ceraioaia iricoloVy from the second thoracic and first abdominal seg- 
ment; b, tliose on the first and second abdominal legs. 
