DEVELOPMENT OF THE EMBRYO. 13 



small an object, did not deter me; for I regarded the 

 cutting into an unbroken series of sections as abso- 

 lutely essential to gaining an accurate knowledge of 

 the formation. 



The reagents and methods which I employed were 

 not the same for all the stages. 



I next made a thorough study of the segmentation 

 in the living object. For this part of the develop- 

 ment such method would be quite sufficient were it 

 not for the unfortunate circumstance that the segmen- 

 tation takes place at night, and therefore can only be 

 studied by artificial light. Some control should be 

 had over such observation through investigation of 

 preserved material to be undertaken by day. 



My drawings of the segmentation stages have been 

 all taken from the living object by means of the Camera 

 lucida. This, I must say, caused me some difficulty on 

 account of the double illumination required for the 

 microscope and for the drawing ; it was too trying for 

 the eye. My results I merely tested 011 material that 

 I had preserved. 



In studying the segmentation, it is most important 

 to gain a view of the objects from different sides by a 

 careful movement of the cover-slip, and especially to 



