THE BEGINNINGS OF LIFE. 211 



properties of the matter of which the ovum is composed. 

 This, too, was the view expressed by Professor Huxley 

 when he said *, c Neither is there any evidence that any 

 attraction or other influence is exercised by the one 

 over the other; the changes which each subsequently 

 undergoes, though they are in harmony, having no 

 causal connexion with one another, but each proceed- 

 ing, as it would seem, in accordance with the general 

 determining laws of the organism. 5 Nevertheless, from 

 the yolk-mass itself (constituted, as we have seen, 

 by a mere aggregation of granules, or by an increasing 

 mass of granular mucilage) there is produced, as a result 

 of this segmentation, the germinal or c blastodermic' 

 tissue 2 , out of which, by a continuous series of changes 



1 Essay previously quoted, ' British and Foreign Medico-Chirurgical 

 Review,' October 1853, p. 386. 



2 Dr. Thomson says : ' The last result of the segmentation is the 

 production of the blastoderma or germinal membrane in which, by 

 other changes, the rudiments of the embryo subsequently make their 

 appearance. According to most ovologists, the last globules formed by 

 segmentation are the nucleated organized cells immediately constituting 

 the blastoderma. But a different view of the process, as it occurs 

 in Mammalia, has been taken by Bischoff, and is very decidedly set 

 forth in his two most recent works on the development of the guinea- 

 pig and the deer respectively. In these memoirs he makes the 

 announcement that ' the last resulting spherules formed by segmentation 

 are not true cells, and that previous to the formation of the blastoder- 

 mic cells the yolk-germ falls completely into an amorphous or homo- 

 geneous finely granular substance, out of which, secondarily, the blasto- 

 derrnic cells are produced by a process of cyto-genesis. It seems 

 probable that, in the different classes of animals, there may be consider- 

 able variety in the degree of perfection in organization or advance in 

 cell structure to which the segments of the yelk have attained at the 



P 2 



