FERTILIZATION AND CLEAVAGE 89 



results in no great acceleration of cleavage since the growth 

 rate remains at about the level of the other slow-cleaving 

 species. The writer has transplanted mouse ova into the 



28 



20 



20 40 60 80 



Fig. 29. Showing the cleavage rates of tubal ova in various species of mam- 

 mals. Abscissa: time in hours after copulation. Ordinate: number of cells. 

 The rabbit = data of Gregory, 1930, and Pincus, 1930. The monkey = data 

 of Lewis and Hartman, 1933. The guinea pig = data of Squier, 1932. The 

 mouse = data of Lewis and Wright, 1935. The rat = data of Gilchrist and 

 Pincus, 1932. The pig = data of Heuser and Streeter, 1929. 



fallopian tubes of the rabbit and has noted no increase in 

 the cleavage rate over a period of 72 hours. 



Castle and Gregory (1929; also Gregory and Castle, 1931) 

 have, in fact, found certain definite congenital differences in 

 cleavage rate between different races of rabbits. A resume 

 of their data is given in Table XVI. The animals of their 

 large race (A) attain an average adult weight of about 

 5500 grams in females and 5400 grams in males. The cor- 



