DEPARTMENT OF EXPERIMENTAL EVOLUTION. 129 



those given by D. anipelophila. A second species being bred has four pairs of 

 chromosomes also, but of a different sort (No. 2). In this the minute pair is 

 lacking, and there are two small pairs in place of one large pair of the previous 

 group. The linkage phenomena should be quite different here. A third 

 species resembles the last, but has the minute pair present (No. 3). This is 

 the species which is especially favorable for cytological study in the male, and 

 I am laying particular emphasis on it. Already one character has appeared 

 which seems to be a mutation, although further breeding is necessary to 

 make it certain. The fourth species has 6 pairs of chromosomes (No. 4), all 

 of which are relatively short. This species should give six groups of linked 

 characters as contrasted with 4 or 5 in the others, and the linkage should be 

 very 'close,' since the chromosomes are short. In this species a definite 

 mutation has just arisen, out of many thousand flies examined. Only the Fi 

 has been secured, but the character appears in this, leaving no doubt about the 

 reality of the 'mutation.' The 4 chromosome groups are shown diagram- 

 matically in figure G. 



Fig. 6. 



' Tf mutations of similar sorts appear in the different species, as I am confident 

 will be the case, a further and much more detailed analysis can be made, and 

 the relation between homologous chromosomes in different species can be 

 shown. 



"While engaged in working out methods for handling Drosophilas I have also 

 experimented with methods for breeding larger flies of various species. This 

 work has resulted in satisfactory methods for rearing 6 or 8 species of the so- 

 called 'higher flies,' and has furnished large amounts of cytological material. 

 It has not seemed advisable to carry these cultures further this year, except 

 for the provision of cytological material. 



"As an auxiliary investigation, quite aside from the Diptera work, I am 

 breeding beetles of the genus Bruchus {B. quadrimaculatus, the cow-pea beetle). 

 The material shows a great range of color patterns and offers excellent oppor- 

 tunity for some phases of breeding. Two generations have been secured thus 

 far (3 months) from an originally mixed stock, and different lines are becoming 

 purified. When this process of selection is completed, the inheritance of the 

 characters will be tested by crossing. Nothing very definite can be said about 

 the results as yet, except that either a large number of factors is involved, 

 or else some very changeable factors are operating. Cytologically the species 

 is good for study, but the number of chromosomes is far too great to allow of 

 such work as is being done with the Drosophilas." 



