MOVEMENTS AND FOLDINGS 



51 



ous dyes ; the other is to take cinematograph photos 

 of the development. The cinema photography can be 

 done in two ways : Graper removed part of the 

 shell over the embryo, stained the whole embryo 

 with a non-poisonous dye so as to make it easier to 

 see, and photographed it by reflected light: while 

 Waddington and Canti took the whole embryo out 



EMBRYO 



WATCH GLASS 



PETRI DISH 



COTTON 

 WOOL 



WATER 



NUTRITIVE 

 MEDIUM 



Fig. 12. — Glass culture vessel for growing embryos. 



of the shell, cleaned the yolk off it, and put it on 

 the surface of a nutritive jelly in a culture-vessel 

 (Fig. 12), where it went on growing and developing 

 and could be photographed as a transparent object. 



When the egg is laid, then, the blastoderm has 

 already developed for several hours after being 

 fertilized in the body of the mother, and consists of 

 a circle of transparent tissue surrounded by a ring 

 of opaque tissue, both these areas being two-layered. 

 The first thing that happens is that some of the 

 ectoderm-cells collect together into a thickening 

 which appears in the posterior part of the trans- 

 parent area, and grows forward till it stretches as a 



