85 
undergoes during the formation of the tadpole. 
Fig. 8 . Some ova after being immersed in water for four- 
teen days ; natural size. 
Fig. 9 - One of them magnified five diameter. 
Fig. lo. The same ovum magnified ten diameters. 
Fig. 11. The same ovum opened; its contents still fluids 
in which oil is found ; magnified ten diameters. 
Plate VI. 
Fig. 1. Ova six hours after being spawned on water; 
natural size. A. one of these ova ; magnified five diameters. 
B. The same ovum magnified ten diameters. C. Longitu- 
dinal section of the same ovum ; its contents in a half coagu- 
lated state, and putting on an organized structure ; magni- 
fied ten diameters. 
The rest of the ova spawned at the same time were kept 
in water, to watch the progress of the formation of the 
tadpole. 
One of these was not impregnated, consequently remained 
unchanged, while the others became gradually more and 
more organized. This abortive ovum is placed at the top of 
each cluster with a mark # 
Fig. 2. The cluster of ova 12 hours after being spawned, 
diminished by that examined in fig. 1. ; of the natural size. 
A. One magnified five diameters. B. The same magnified 
ten diameters. C. The same, forming a longitudinal section ; 
magnified ten diameters. 
. Fig. 3. Twenty-four hours after being spawned. 
Fig. 4, Thirty-six hours after being spawned. At this 
period the ovum has its form considerably changed, and the 
head and tail of the tadpole are distinctly seen. 
