392 
J. F. McClendon 
were classified as normal tadpoles (except in coloration), abnormal tad- 
poles, partial embryos and irregulär cleavage stages. In tlie list below, 
the numbers refer to the succession of ten minute periods : 
1 normal tadpoles 
2 » » 
3 » » 
4 » » 
5 abnormal tadpoles 
6 » » 
7 » » 
8 » )> 
9 » » 
10 » » 
11 irregulär cleavage pro-nucleus seen in sections) 
12 » » 
13 normal tadpoles 
Commencement of first eleavage furrow 
14 normal tadpoles 
15 irregulär cleavage 
16 normal tadpoles 
17 partial embryos 
18 normal tadpoles 
19 » )) 
Commencement of second cleavage furrow 
20 normal tadpoles 
21 partial embryos 
22 » )) 
23 » » 
Commencement of third cleavage furrow 
24 abnormal embryos 
25 irregulär cleavage. 
In a second set of experiments, lots corresponding to lots 20 — 25 in 
the above list all gave partial embryos as the best results. Although 
the results are not quite uniform, it appears that the early stages after 
the eggs are laid, as indicated by the first ten lots, are less affected by 
centrifugal force than later stages. I attribute this to the fact that the egg 
is more viscid in early stages and consequently the stratification of sub- 
stances and production of currents is less than in later stages. Thus I 
found that the time required to stratify the ripe ovarian egg by means 
of a given centrifugal force to be much greater than that required during 
