THE DARWINIAN THEORY. 



87 



comb an entirely new (" walnut") comb results, whicb has 

 bristle-like bairs ; the proportion of walnut, pea, and single by 

 this mating being as 9:3:3:1. These complex phenomena 

 are supposed to be due to compound allelomorphs in contrast 

 with others in which simple allelomorphs only are present 

 in the ova.* Selection, in certain cases, the Mendelians affirm, 

 will never make a form breed true. Some Darwinians severely 

 criticise the methods of the Mendelians and Mutationists in this 

 country, and hint that instead of aiding in the work of eluci- 

 dating evolution they appropriate much that is Weismann's and 

 hinder progress. 



Besides the foregoing much also has been observed and 

 written concerning Heredity! since 1859, the problem being as 

 to " How it is that a single germ-cell can produce, by repeated 

 division, an organism in which the peculiarities of the somatic 

 units of the parent are reproduced?" (Poulton). Among the 

 most conspicuous efforts to solve it is Weismann's theory of 

 " The Continuity of the Germ-Plasm," or the blastogenic theory, 

 which is in contrast to the somatogenic or theory of Pangenesis 

 of Darwin, in which every somatic cell is a germ-cell, the germ- 

 cells proper being the central meeting-place.] 



Darwin points out in the next place that variation occurs 

 amongst animals and plants in a state of nature. One of the 

 most remarkable-of such variations is that recently described by 

 Mr. Bates as occurring in the butterflies of the great Valley of 

 the Amazon. He observed that a gregarious butterfly (one of 

 the Heliconidce) swarmed in incredible multitudes. In these 

 swarms are to be found in small numbers other species of 

 butterflies belonging to at least ten genera and some moths, and 

 these intruders, though structurally different, mimic the mem- 

 bers of the great group with which they associate so closely that 

 it is a most difficult thing to distinguish them. That they are 

 really intruders is shown by the fact that these mimickers de- 

 part from the usual colours of their genera. Moreover, they 

 evidently do so to escape destruction by birds and other animals, 

 for Mr. Bates found that the species of the large group which 

 they mimic are seldom or never preyed on, as he thinks, on 



* Vide an interesting epitome of Mendelisrn by Mr. R. C. Punnett, 1905. 

 f Vide the excellent treatise on • Heredity ' by Prof. Arthur Thomson, 1908. 



