STRUCTURE AND GROWTH OF DOMESTICATED ANIMALS. 655 
chicken, or the little turtle. Compare in this respect the figures 
of D’Alton with those of Bischoff and my own in the embryology 
of our terrapene. 
Now, what are the conditions necessary for making these obser- 
vations? A man must be practised, and not only practised, but 
fully skilled in the use of the microscope. He must know the 
structure of the animal in its adult condition so accurately, and so 
completely, that every difference in the structure of the younger 
animal will at once strike hiseye. He must be able to make these 
comparisons without having specimens before him for-comparison ; 
Young Blenny, copied from Rathke’s Embry- Thesame as fig. 170, seen in profile from the 
ology of the Zoarces viviparus. Magnified. left side. 
; Seen in profile from the right side, 
3 Fig. 172. . Fig. 173. 
The same as figs, 170 and 171, seen in front. ige kere ha figs. 170; 171 and 172 before the 
he must have appropriated that knowledge to himself so com- 
Pletely that he may weigh the changes going on in the substance 
of the germ, merely by the eye, and ascertain every change in so 
accurate a manner that he may record the facts in their true con- 
nection. And more than that, he must be able to prepare the 
Conditions in which these germs will not be altered by being 
brought under the microscope. Try to bring an embryo, a young 
chick, in that early stage of growth, as you see it after a few 
days’ incubation, under the microscope, and you are likely to find 
