188 ' BEPOKT— 1891. 



into smaller elements like the male cells, this tendency being 

 still represented, however, by the throwing-off of the polar 

 bodies. 



Attraction between male and female cells, at first of a 

 chemical nature, led to their fusion, which was favoured by 

 the similarity of their protoplasm, and by the need, on the 

 part of the male cell, for more cytoplasm. 



The result of the increase in size of the cytoplasm of the 

 ovum is that, after fusion of male and female cells, a series of 

 segmentations are set up which result in the development of 

 an embryo. This is rendered possible by the large size of the 

 cell-body of the ovum, by which a field was afforded for 

 nuclear motion and growth. 



" The principle of continuous growth through cumulative 

 integration ; its rhythmical interruption through the ' setting- 

 aside,' or dehiscence, of the useless sexual elements; the 

 evolution of a cytoplasmic field ; the direct adaptation to their 

 surroundings of colonial aggregates of cells, resulting from the 

 coherent segmentation of masses of plasma resulting from 

 reciprocal integration ; the necessarily cumulative super- 

 imposition of adaptations upon one another, have been, in 

 the main, the materials upon which natural selection was 

 dependent in order to become operative in biological evolu- 

 tion." 



It is indicative of the very great difficulties which the sub- 

 ject presents that to this day there exist differences of an 

 almost radical character between the views of the minute 

 structure of cell-protoplasm held by different histologists who 

 have devoted attention to this matter. The most generally 

 accepted statement is that there are two kinds of protoplasm 

 present in every cell: a more fluid kind (hyaloplasm), and a 

 kind of a less fluid character (spongioplasm), the latter taking 

 the form of a denser or more open network of threads, between 

 the interstices of which the former lies. There is evidence of 

 this from the appearances presented by many dead and stained 

 cells and a few living ones. iVccording to Biitschli,''' however, 

 this is not the true way of viewing the constitution of the cell- 

 protoplasm. The two components are rather to be regarded 

 as mixed together : the one substance — the hyaloplasm — in a 

 state of fine division, and disseminated through the spongio- 

 plasm like the oily matter in an emulsion. Biitschli recognises 

 the presence, in many cells, of stiffer trabeculae and threads in 

 the spongioplasm, which often form networks ; but he regards 

 these as not essential to the structure of living protoplasm, 

 since in many cells, e.g., Ammbce, they are not present. 



• " Miissen wir cin Wachsthum des Plasmas durch Intussusception 

 annehmen ? "— " Biol. Centralblatt." 8 Bd., pp. 161-164, 



