322 THE POPULAR SCIENCE MONTHLY 



We can not, however, consider this more than a slight alteration 

 from the normal condition for two reasons. First, because the silk- 

 worm is closely allied to forms of moths in which parthenogenesis is 

 normal ; and second, because, as Loeb states, " Siebold had already men- 

 tioned, and Nussbaum confirmed his observations, that a small num- 

 ber of such eggs develop without these means." This is about the last 

 we shall hear of artificial parthenogenesis, as our review takes us higher 

 and higher in the organic scale of evolution. The results of such at- 

 tempts as have been made to induce this form of modification among 

 the vertebrates have been very unsatisfactory. Nothing can be made 

 to develop beyond the segmentation stage. 



Some experiments like those of Dorfmeister, Weismann, Eimer, 

 Merrifield and Poulton show the direct results of changes in tem- 

 perature, food and even the color of the surroundings; but these affect 

 the character of the pigmentation in these normally highly pigmented 

 forms, and we shall see, as we go higher in phylogeny, that pigmenta- 

 tion is one of the easiest characters to alter through environmental 

 differences. 



Eegeneration experiments are naturally not numerous on the bodies 

 of insects, for practical reasons, but their power to regenerate lost 

 legs and wings falls in line with our generalization. The legs of the 

 lower insects, like the walking-stick and cockroaches, will grow again 

 if amputated, the legs of the higher insects, butterflies, ants, bees and 

 wasps, not so well. Larval insects are placed by Przibram about on a 

 par with adult mollusks, leeches and fishes, and a little behind Amphi- 

 oxus as far as general power of regeneration is concerned. Insects in the 

 final or adult stage are placed in the highest class along with mammals 

 and birds, but since adult mammals and birds can not regenerate 

 lost limbs 20 it seems as if further subdivision might have been made. 

 Experiments which consist of grafting parts of different species on 

 to one another are possible among insects at least during the pupal 

 stage. 21 But the " integumentary organs " alone show successful union. 



There is one way in which insects appear to show less modification 

 than the vertebrates. Eemoval of the sexual glands from birds and 

 mammals produces, as is well known, certain marked anatomical and 

 physiological changes. These are supposed to be due to the cessation of 

 an internal secretion which the gland normally produces. Removal 

 of the sexual glands from insects does not cause changes in the sec- 

 ondary sexual characters. It seems fair to assume that this is because 

 the sexual glands of insects do not produce any internal secretion. If 



20 " Experimental Zool.," " Eegeneration/' Taf. XVI. Die hochsten Formen 

 regeneriern bloss Gewebsdefekte und ungegliederte einfache Hautbildungen 

 (Schnable, Insektenfliigel ) . For aid in interpreting experiments on insects I 

 am also indebted to Professor W. M. Wheeler. 



21 Morgan, "Exp. Zool.," p. 301. 



