772 PROCEEDINGS OP THE AMERICAN ACADEMY. 



designated later as " Families A, B, and C," were carried through, each 

 having as parents a brother and sister belonging to the fifth genera- 

 tion. All of the flies appearing in these cultures were preserved in 70 

 per cent alcohol, so that the whole number of offspring was obtained. 

 The parents were well supplied with food and kept until they died. The 

 female parent of each culture was transferred at the end of about every 

 ten days to a new jar. Imagoes began to appear in the first jar while 

 the female parent was still alive and laying eggs. 



A control stock culture was maintained during the year under a large 

 bell-jar. Here the flies were allowed to breed without interference. 

 They required no care except to be provided from time to time with 

 fresh food. 



(a) Effect on fertility and sexual proportion. In the three cultures 

 of the sixth generation designated " Families A, B, andC," all the off- 

 spring were saved. The numbers of these and their sexual proportions 

 were as follows : 



No accurate determinations were made of the number of offspring of a 

 normal pair of flies, but from such observations as were made it is 

 probably safe to say that no striking falling off in fertility is to be seen 

 in the sixth inbred generation. No indication of weakness was observed 

 among the flies. 



Since the sexual proportion is near equality (possibly with a slight 

 excess of males), the figures given above indicate, on the whole, no 

 marked change in this respect. 



(b) Effect on variability. The number of teeth was counted in the 

 eighty sexual combs of forty males taken at random from the control 

 stock culture, and the results were plotted in the form of a frequency 

 polygon (Figure 5, N). In addition the teeth were counted in the same 

 number of combs in the case of each of the inbred cultures, A, B, and 

 C. These results were also plotted in frequency polygons (Figure 5, 

 A, B, C). 



It will be seen that the number of teeth in the sexual comb is higher 

 in all the inbred families than in the normal flies (N) studied. Both 

 means and modes are higher for the inbred flies. But it is doubtful 

 whether this is the result of inbreeding, for the male employed in start- 



