THE DEVELOPMENT OF THE EMBEYO ITSELF. 



We now turn to the development of the body of the animal 

 for which the structures we have been describing exist. It is 

 important, however, to remember that the development of 

 parts, though treated separately for the sake of convenience, 

 really goes on together to a certain extent ; that new structures 

 do not appear suddenly but gradually ; and that the same law 

 applies to the disappearance of organs which are being super- 

 seded by others. To represent this completely would require 

 lengthy descriptions and an unlimited number of cuts; but 

 with the above caution it is hoped the student may be able to 

 avoid erroneous conceptions, and form in his own mind that 

 series of pictures which can not be well furnished in at least . 

 the space we have to devote to the subject. But, better than 

 any abstract statements or pictorial representations, would be 

 the examination of a setting of eggs day by day during their 

 development under a hen. This is a very simple matter, and, 

 while the making and moimting of sections from hardened 

 specimens is valuable, it may require more time than the 

 student can spare ; but it is neither so valuable nor so easily ac- 

 complished as what we have indicated ; for, while the lack of 

 sections made by the student may be made up in part by the 

 exhibition to him of a set of specimens permanently mounted 

 or even by plates, nothing can, in our opinion, take the place 

 of the examination of eggs as we have suggested. It prepares 

 for the study of the development of the mammal, and exhibits 

 the membranes in a simplicity, freshness, and beauty which 

 impart a knowledge that only such direct contact with nature 

 can supply. To proceed with great simplicity and very little 

 apparatus, one requires but a forceps, a glass dish or two, a 

 couple of watch-glasses, or a broad section-lifter (even a case- 

 knife will answer), some water, containing just enough salt to 

 be tasted, rendered lukewarm (blood-heat). 



