200 THE entomologist's RECORD. 



experiments that the numerical results could be handled in precisely 

 the same way as are other linkage results. 



Whilst steadfastly pursuing the main objects of their investigation, 

 the authors were on the qui vii-e for any items which bore on the most 

 important unsolved biological problems. The Drosojihila appeared to 

 be particularly sensitive to environment in its early stages. In a 

 certain environment, kept uniform, a particular character called 

 "abnormal abdomen" can be induced, which is gradually lost in 

 subsequent generations, when the environment becomes gradually 

 normal, but recurs with the imposition of the former environment. 

 This was repeated several times for many generations of the Droso- 

 imila. Here then was a character which is readily susceptible to 

 change of environment, yet, apparently, the conditions had no effect 

 whatever on the nature of the germ-plasm, as there was no trace of 

 the abnormality remaining after the altered conditions were removed 

 and the environment became normal. It is claimed from this that 

 " A more striking disproof of the theory of the inheritance of acquired 

 characters would be hard to find." The indirect influence of environ- 

 ment on sex-linked abnormality is also dealt with. 



It is suggested that these experiments may afford another explana- 

 tion of the remarkable cases of polymorphism in animals with more 

 than one kind of female, or male, which Darwin and his followers 

 say might arise through natural selection. A group of characters in 

 Drosophila is pointed out as a parallel case to that which occurs in 

 Colias philodice, where there is one type of male, yellow, and two types 

 of female, yellow or white, in Colias eurydice where the male is orange 

 and the female orange or white, or in Papilio turn us where the male is 

 yellow, the female yellow or black. 



Among other points dealt with is "Fertility and Sterility in the 

 Mutants," on which the evidence is inconclusive so far. 



At any rate the serious charge which was once made against a 

 previous work of the authors that " the material for such an examina- 

 tion is not contained in it," cannot be made here, for the bulk of the 

 book, some sixty pages, is taken up with the data of all the more recent 

 experiments upon which the argument of the authors is based. There 

 are two coloured plates illustrative of the mutant characters of the 

 Drosophila, and a Bibliography of what has been published since 1910 

 on this special line of enquiry. 



Results such as those recorded in this work, based as they are upon 

 enormous numbers of individual objects, cannot be ignored as being on 

 slight foundation. We congratulate the authors on the persistent 

 effort which they have so long sustained in a most tedious task, and 

 also more than a considerable meed of praise is due to them for the 

 acumen with which they have perceived the bearing of the results, not 

 only direct, but indirect, on points and questions of biological import- 

 ance, which were not the special object of their experiment and 

 research. To quote the words of Professor Bateson, "Let it be 

 explicitly said that not even the most sceptical of readers can go 

 through the Drosojihila work unmoved by a sense of admiration for the 

 zeal and penetration with which it has been conducted, and for the 

 great extension of genetic knowledge to which it has led — greater far 

 than has been made in any one line of work since Mendel's own 

 experiments." — H.J.T. 



