H. M. FiTCHS J+O 



series correlated with the decrease in th(> latter. Moreover in the first 

 series, although thi' segmentation became more rapid in later fertili- 

 zations, the time taken to complete the 4-cell division was longer than 

 that of the slowest segmentation in Series C. Nevertheless the tem- 

 perature during the latter was throughout lower than during the fomner 

 series of experiments. The possibility is, however, not excluded, and 

 unfortunately time would not allow of a fiirther investigation. Never- 

 theless the difference in behaviour of the eggs would seem to depend 

 rather on some condition of the animals from which they are taken. 

 The four series were made on four different days, and each with a 

 different batch of animals brought into the laboratory. This, taken 

 together with the fact that the experiments of each series agreed in 

 general with one another, seems to support this view. 



2. Eg(js and sperm from different parts of genital ducts. 

 During the experiments made to investigate the effect of the " age " 



of eggs and sperm, as indicated by their relative position in the genital 

 ducts, on the extent of self- and cross-fertilization, the segmentation 

 rates of the fertilized eggs were noted. The lengths of time after 

 fertilization at which the first 4-cell divisions took place are recorded in 

 Table VII ( p. 239) for some of the lots of eggs. 



A comparison between the times taken by 6* eggs cross-fertilized : 

 (1) by sperm a, from the base of the sperm duct, and (2) by sperm a„ 

 from the top of the sperm duct, in Exp. 1, shows that the segmentation 

 rates were identical, although the percentages of eggs fertilized were 

 very different in the two cases. Again, eggs from (1) base, (2) middle, 

 and (3) top of the oviduct cross-fertilized by the same sperm, all segment 

 at the same rate, although the jiercentages fertilized may be different. 

 This is shown by the segmentation times in Exp. 1, cross Ajm and 

 Exp. 2, cross Bjn of Table VII. 



Thus, neither the position in the genital duct of the sperm used to 

 make a cross, nor that of the eggs crossed causes any variation in the 

 early rate of division of the segmenting eggs. 



3. Gojnparison of development after self- and cross-fertilization. 



The first experiment consisted in a comparison of the segmentation 

 rates of (1) eggs self-fertilized (Kjk), (2) eggs of the same individual 

 cross-fertilized (K/p), and (3) eggs of another individual cross-fertilized 

 by the same sperm as that used for the self-fertilization {L(k). In each 

 case the eggs were fertilized at four different intervals after the genital 



