The Process of Heredity 541 



verbal description could, how real a difference exists between 

 pure and hybrid strains at these stages (Figs. 9, 10, 11 and 12). 

 Set I : Killed after 56 hours, ten embryos of each strain pre- 

 served. Numbers of somites: 



impure: 10, 9^, 10^, 10, 10, io|, 10, io|, 9I, 10. Average 



10 + . (Fig. 9.) 

 H hybrid : 5^, 7I, 6, none, 6, 4, 6§, 6|, 5I, 6. Average 5.3. 



(Fig. 10.) 

 M hybrid: 6, 3, 2, 2, 3, the rest none. (Fig. II.) 

 M pure: none in any of the specimens. (Fig. 12.) 



The figures show an average condition in each case. 

 Set 2: Ten of each strain killed after 86 hours. Numbers of 

 somites: 



H pure: 21, 2i, 2i, 21, 20, 21, 21, 21, 21, 20. Average 



20.8. 

 //hybrid: 15, 16, 17, 16, 15, 16, 14, 15, 17, 12. Average 



I5-3- 

 M hybrid: 14, 15, I2, 16, 16, 16, 16, 16, 17, 16. Average 



15.4. 

 M pure — 13, 13, 13, 13, 13, 13, 12, 13, 13,1 2. Average 12.8. 



Set 3 : Killed after 48 hours, ten embryos of each strain preserved . 

 As there were no somites another index of development was chosen. 

 Four stages of development were arbitrarily chosen and drawn 

 (Figs. 13, 14, 15 and 16). Then the various specimens were 

 referred to the stages by number. When the condition fell between 

 two numbered stages the figure ^ was used to express the inter- 

 mediate condition. The results were as follows: 



H pure: 4, 3I, 3I, 4, 3^, 4I, i|, 3^, 4, 4. Average 3.6. 

 H hybrid: i, 2, 2^, 4, 2^, 2, 2, 2^, 4, 4. Average 2.65. 

 M hybrid : 2, 2\, 2\, 2, i, 2, i|, i, 2, 2, i. Average 1.95. 

 M pure: i, i, i\, i, i, i, 2, i, i, i. Average 1.15. 



Several other sets showed practically the same facts as those 

 just detailed. Later stages do not make favorable whole mounts, 

 on account of their opacity. 



