1 86 THE BEGINNINGS OF LIFE. 



owing apparently to the darker granules accu- 

 mulating in the form of zones between them 

 as in the formation of the spores of Hydrodictyon. 

 Later still, a redispersion of these granules takes place, 

 leaving light streaks, instead of dark granular boundary 

 lines, between what are to be the future spores. Then 

 a solution of continuity is gradually effected, between 

 the several spores, in the situation of these light streaks, 

 and also between them and the membrane of the spore 

 case, till the whole of the contained protoplasmic 

 matter has thus been broken up into moving re- 

 productive bodies. 



The phenomena taking place within the spore-cases 

 of Lichens are essentially similar. It is stated by 

 Pineau l that the process can be best watched in 

 Physcia dl'taris, on account of the large and transparent 

 nature of the spore cases in this species. The first 

 step in the formation of the spore in this plant is 

 said to be the formation of aggregations amongst the 

 granules which had been previously dispersed through- 

 out the mucilaginous contents of the spore-case. These 



the conclusion that such was the mode of origin of the nucleus in the 

 white blood corpuscle. (See p. 227.) Here, as in other cases, the definite 

 bounding-wall of the nucleus is, like the cell-wall itself, an after pro- 

 duction. 



In certain cases the nucleus makes its appearance before the com- 

 plete individuation of the embryo cell has taken place, but, just as 

 frequently (as is the case with white blood corpuscles), the nucleus 

 appears, after the fashion above indicated, in an already isolated non- 

 nucleated embryo cell, or plastide. 



1 ' Ann. des Sc. Naturelles,' 1848, p. 99. 



