MEMOIliS OF THE NATIONAL ACADEMY OF SCIENCES. 33 



v.— ON THE IXHERITAXCE OF ACQUIRED CHARACTERS I\ LEPIDOPTERA. 



Perbaps in no other group or order of auimals may we study tlie subject of tlie inlieritance of 

 acquired characters with more success than in the Lepidoptera. In these insects the four stages 

 of existence — tlie egg', hirva, pupa, and imago — are definite and fixed, and during each of the three 

 last periods the organism is, so to speak, a diflereut creature, witli distinct and separate shajie 

 and structure, external and internal, and during each leads a different life. Family, generic, and 

 specific characters are inherited at each of these stages, and at each there is a combination of 

 congenital and acquired characteristics, some of both classes of which, i. c., those least marked, 

 are difficult to separate from each other. 



Tlie following is an attempt at a rough grouping of such features at the last three stages. "We 

 omit the egg stage, for though they more or less vary in shape and ornamentation, this is iierhaps 

 ■due more to difference in the structure of the lining of the oviduct of the female than to the action 

 of external circumstances on the egg after it has been laid. Yet this should be said with some 

 reservation, because we are not aware that any one has discussed the probable mode of origin of 

 the specific differences in the shape and color of the eggs of birds or the shape and markings of 

 the eggs of insects, though undoubtedly the agency of external causes, together with natural 

 selection, has had something to do with the variation. 



It has seemed to us that the relation of specific and generic characteristics in the eggs of 

 insects is a most difficult problem. Y^et it should be observed that while the differences in orna- 

 mentation and shape are primarily due to the imiiression on the shell received from the lining of 

 the oviduct, yet the woii;lerful diversity we see in the eggs of insects is often readily seen to be 

 correlated with the external conditions in which they exist after having been deposited by the 

 parent. In birds the thick, solid shell and the oval shape of the murre's egg seem due to the 

 unprotected manner in which they are left on the rocks and shelves, from which they are liable 

 to fall. 



We may contrast with such an egg that of the robin, in which tlie shell is thin and uniform 

 in color, since it is protected from harm by being contained in a nest; so also the color of the 

 murre's eggs may be due to the action of protective mimicry, the spots assimilating them to lichen- 

 grown rocks, by which they escape the observation of their natural enemies, the fox, the mink, 

 and other egg devouring animals. So the eggs of Chrysopa, of many bugs, etc., are in shape and 

 mode of attachment beautifully adapted to prevent them from being seen by egg-devouring 

 animals. 



In the larval histories given in this work we have endeavored, where they have been observed 

 with sufficient completeness, to discriminate between the congenital and the acquired characters. 



1. Larval state. — A. In this state we have the inheritance of congenital characteristics. 



B. Inheritance of what were originally acquired characters, the results of attacks of enemies: 

 Exampjes are the tubercles armed with sx^ines and sometimes with caltrops (Empretia, etc.) and 

 stripes, all ajiparently inherited at different periods of larval life, the least important specific 

 and varietal characters probably having been acquired during the life of an .individual. 



3. Pupa state. — A. Cocoon: The absence or presence of a cocoon was doubtless originally due 

 to differing external conditions, while the dense, perfect cocoon is characteristic of the spinning 

 moths (Attacida', Lasiocampidw, etc.) ; the Ceratocampidte make none at all, but, like the Sphinges, 

 the larvfe simply bury themselves in the earth before pupation. In the Arctiidte and the Lipa- 

 rida^ the cocoon is chiefly composed of the barbed larval hairs, with a little silk to fasten them 

 more firmly together; in the Geometrida^ certain larva- spin a loose, thin web. In such cases the 

 spinning of a cocoon is intimately associated with a change of larval habits, and is, with little 

 doubt, an acquired habit, originally formed by a single individual. 



B. The shape of the pupa is often dependent on the presence or absence of a cocoon. In the 

 Notodontidse the cremaster is often absent in genera such as Gluphisia, which spins a very slight 

 cocoon, and Lophodonta, which spins no cocoon, and is closely allied to those which do. In 

 Cerura there is no spine on the rudimentary cremaster, because the i)upa lies in a very dense 

 •cocoon fastened to the bark of trees, etc., and being in no danger of being shaken out no cremas- 

 S. Mis. 50 3 



