370 THE EVOLUTION THEORY 



the germ must differ in size, according as we have to do with an 

 organism which is small or large, simple or more complex. Uni- 

 cellular organisms, such as Infusorians, probably possess special 

 determinants for a number of cell-organs and cell-parts, although we 

 cannot directly observe the independent and transmissible variation 

 of these organs ; lowly multicellular animals, such as the calcareous 

 sponges, will require a relatively small number of determinants, but 

 in the higher multicellular organisms, as, for instance, in most 

 Arthropods, the number must be very high, reaching many thousands 

 if not hundreds of thousands, for in them almost everjrthing in the 

 body is specialized, and must have varied through independent 

 variation from the germ. Thus in many Crustaceans the smelling- 

 hairs occur singly on special joints of the antennae, and the number 

 of joints furnished with a smelling-hair is different in different 

 species ; the size, too, of the smelling-hairs themselves varies greatly, 

 being, for instance, much smaller in our common Asellus than in the 

 blind form from the depths of our lakes, in which the absence of sight 

 is compensated for by an increased acuteness of the sense of smell. 

 Thus the smelling-hairs may vary transmissibly in themselves, while 

 any joint of the antennae may also produce one independently 

 through variation. In this case accordingly we must assume that 

 there are special determinants for the smelling-hairs, and for the 

 joints of the antennae. But we cannot always and everywhere refer 

 identical or approximately similar organs, when there are many of 

 them, to a corresponding number of determinants. Certainly the 

 hairs of mammals or the scales of butterflies' wings do not all vary 

 individually and independently, but those of a certain region vary 

 together, and are therefore probably represented in the germ-plasm 

 by a single determinant. These regions often appear to be very small, 

 as is best seen by the fine lines, spots, and bands which compose the 

 marking of a butterfly's wing, and still more in the odoriferous scales 

 occurring in some butterflies, as, for instance, in the blue butterflies 

 (Lycaina). These little lute-shaped scales do not occur in all species, 

 and they occur in very unequal numbers even in those which possess 

 them ; there are certain species which exhibit only about a dozen, and 

 these are all on one little spot of the wing. Since these odoriferous 

 scales must have arisen as modifications of the ordinary hair-like 

 scales, as one of my pupils. Dr. Kohler, has demonstrated by compara- 

 tive studies, these ordinary hair-like scales must have varied trans- 

 missibly at certain spots, that is, their determinants have varied while 

 those of the surrounding scales have not. 



The case is the same in respect to the sound-producing apparatus 



