248 THE BEGINNINGS OF LIFE. 



began to undergo other heterogenetic changes. This 

 was first indicated by an increased refractiveness of 

 the area (especially when seen a little beyond the focal 

 distance), and almost simultaneously a condensation of 

 its outer layer seemed to take place, whereby the out- 

 line became sharply and evenly defined 1 . At this stage 

 an actual membrane is scarcely appreciable, and the 

 substance of the embryo (when examined at the right 

 focal distance) scarcely differs in appearance from the 

 granular pellicle of which it had previously formed 

 part, 



So far as it could be ascertained, the individual 

 embryos did not increase in size, although they went 

 through the following series of developmental changes. 

 The contained matter became rather more refractive, 

 and the number of granules within diminished con- 

 siderably, whilst new particles after a time seemed 

 gradually to appear in what was now a mass of con- 

 tractile protoplasm. These new particles were at first 

 sparingly scattered, though as they were evolved they 

 continued to grow into biscuit-shaped particles, which 

 sometimes attained the size of TtrsoV ' All sizes were 

 distinguishable, and many of them moved slowly 

 amongst one another, owing to the irregular contrac- 

 tions of the semi-fluid protoplasm in which they were 



1 The first changes seem to take place rather rapidly, judging from 

 the great difficulty of recognising the earlier stages. It was almost 

 impossible to find an area which was not already bounded by a delicate 

 outer layer. 



