306 BOAED OF AGRICULTUKE. 



figures of D'Alton with those of Bischoif and my own in the 

 Embryology of our Terrapene. 



Now, what are the conditions necessary for making these 

 observations ? A man must be practised, and not only prac- 

 tised, 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 his eye. 

 He must be able to make these comparisons without having 

 specimens before him for comparison : he must have appro- 

 priated that knowledge to himself so completely 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 connec- 

 tion. 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 find it 

 after a few days' incubation, under the microscope, and you 

 are likely to find that you have reduced it to a shapeless mass. 

 These objects cannot be handled like a piece of wood. They 

 must be treated with a degree of delicacy which makes it im- 

 possible, for instance, for an observer to use any stimulant, 

 even such as cofifee and tea, or to eat heartily, or to exercise 

 in any degree which may accelerate the pulse ; otherwise his 

 eye will be constantly thrown out of focus. Unless a man 

 has himself under control to that extent, he cannot begin to 

 make good observations. Not only must he have the knowl- 

 edge necessary, not only must he have the practice neces- 

 sary, not only must he have the instruments necessary — he 

 must have his own organization so completely under control 

 that he brings himself into that living relation with the 

 object of his observations which alone makes it possible that 

 they shall be accurate. It is not everybody who is willing 

 or able to do this ; and then he must carry on his observations 

 by day and night, as the embryo is growing unceasingly, 

 and unless he does continue his observations uninterrupt- 

 edly, he may miss the most important steps in the prog- 

 ress of growth. Now before you find a man qualified to be 

 an observer, you may have to wait a long while. It was just 



