PACKARD. — INHERITANCE OP ACQUIRED CHARACTERS. 361 



and are closely allied to those which do. In Cerura there is no spine 

 on the rudimentary cremaster, because the pupa lies in a very dense 

 cocoon. The cremaster affords excellent generic and specific charac- 

 ters. In the subterranean pupa of Datana it is present, and is of use 

 in aiding the pupa to reach the surface of the ground. It is very 

 large and acute in the subterranean pupae of Ceratocampidae and 

 Sphinges. It is evident that in the presence or absence of a cre- 

 master, and in its shape, and in the number of hooks and their shape, 

 we have a set of very plastic characters, whose variability and plasti- 

 city are due to the varying habits of the pupa, whether living above or 

 under ground, whether protected by a very thin loose netlike cocoon, 

 or by a solid double one like that of Cerura or of the silk-worms. 

 Also whether the thread is continuous and can be readily reeled, as in 

 Bomhjx mori, or whether the thread is often interrupted at the ante- 

 rior end, as in Platysamia cecropia, is a feature which was probably 

 the result of a slight chauge of circumstances, and may have been 

 inaugurated as the result of variation in a single individual, duriujj a 

 single lifetime, becoming eventually fixed by homochrouic inheritance. 



III. Imago Stage. — It is easier to select what may have been ac- 

 quired characters in caterpillars than in butterflies and moths, and yet 

 the last have a complicated series of what may originally have been 

 acquired characters. It should be borne in mind that, while caterpil- 

 lars live for weeks and even months, are subject to frequent moults, 

 are active and dependent on a proper supply of their food, usually this 

 or that plant, butterflies and moths perish directly after mating, taking 

 little or no food. Of course, acquired characters are most marked in 

 the parts which are most used, as the maxillae, wings, and external 

 genital armature. 



The absence of maxillae, or their very rudimentary condition, in 

 Bombycine moths, is with little doubt a recently acquired character. 

 The very arbitrary distribution in Lepidoptera of scent-organs (andro- 

 conia, etc.) is apparently a character recently acquired. The won- 

 derful variations in the markings of the wings, due to a variety of 

 slight causes, may often arise during an individual's lifetime and 

 become a matter of inheritance, the result of sudden changes in tem- 

 perature, moistness or dryness, and changes in food of the larva. By 

 subjecting individual pupae to prolonged cold or heat, varieties, and 

 a greater or less number of broods, may be produced artificially, and 

 this may illustrate how seasonal varieties have arisen in nature. 



Many species are only separated by differences in the male genital 

 armature. These, as is well known, are subject to great individual 



