REVIEWS. 197 



a superabundance of the limitations necessary, " The animal breeds 

 rapidly, going through many generations in a year. It is inexpensive 

 to breed and the families consist of numbers, which, relatively to those 

 attainable in most subjects, are enormous." Furthermore, " Since it 

 first attracted Professor Morgan's attention it has been found to pro- 

 duce a long and intricate series of factorial varieties or ' mutations,' as 

 the author prefers to call them, differing in the colour of eyes and body, 

 the sizes and shapes of the wings, and other respects, the number of 

 these differences being now computed at more than a hundred. Prof. 

 Morgan and a band of enthusiastic colleagues set themselves with the 

 utmost zeal to analyse the inter-relations of this mass of factors. Half 

 a million flies have been bred, with the result that the data respecting 

 the genetics of Dfosophila in quantity now surpass those obtained from 

 any other animal or plant." As Professor Bateson, whom we have 

 quoted, says, " The advances made are on any estimate many and of 

 quite exceptional significance. That much is certain. If we go further 

 and accept the whole scheme of interpretation without reserve we are 

 provided with a complete Theory of Heredity, so far as proximate 

 phenomena are concerned." 



The interrelation between allelomorphic pairs of different charac- 

 ters has been established by Bateson and others, e.i/., the association in 

 the Chinese Primulas of the allelomorph pair, large eye and small eye, 

 with the allelomorph pair long style and short style. Such a com- 

 bination Professor Morgan has termed " linkage." Cases of such 

 linkage have been found in several forms, but nowhere on so extensive 

 a scale as in the Droftophila, where over a hundred characters have been 

 investigated as to their linkage relations. 



It is a matter of common observation that many characters, 

 especially in animals, " are confined to one sex, or are developed 

 differently in males and females ; this is most conspicuously so in the 

 so-called 'secondary sexual characters,' eu/., the possession of pectinated 

 antennse in male Lepidoptera, the development of frontal processes in 

 male Coleoptera, the hairy growth on the faces of men, etc. That 

 such distinctively male characters are transmitted throiujh the female 

 scarcely needs assertion. Also it is a matter of common knowledge to 

 us as entomologists, that under certain circumstances such male 

 characters may be developed in the female. These characters are not 

 in any way directly connected with reproduction, any more than the 

 character of colour-blindness, which is also similiarly confined to the 

 male sex. These associations of sex and characters have given strong 

 ground for the suggestion that sex is a character subject to the Mende- 

 lian law. On this aspect of the subject the present work of Professor 

 Morgan and his colleague will no doubt have a considerable amount of 

 influence. In fact there has been discovered in this fly, Drosoji/dla, an 

 example of inheritance parallel to that seen in this last instance, colour- 

 blindness in man. Substituting red eye and white eye in the fly for 

 normal colour vision and colour-blindness in man, the phenomena were 

 exactly similar. Hitherto no such case in an animal available for 

 experiment had been known, although we were a wart) of several 

 instances in which the parts played by the sexes were reversed, as in 

 the case of Abraxax i/rosunlariatiu in which the very rare variety larti- 

 color is practically confined to the female sex. 



In the introduction, which comprises some twenty pages, the 



