STEUCTUEE AND EEPEODUCTION 25 



of the nucleus, rendering the mass granular. The 

 external granules of the mass then arrange them- 

 selves -against the nuclear membrane. The central 

 portion of the nucleus then reunites and forms a 

 solid body of chromatin. The result of this move- 

 ment is to draw the peripheral granules towards the 

 centre, and to lengthen them until they are attached 

 by their points only to the external membrane. 

 This results in the formation of little nuclei lining 

 the inner surface of the membrane ; when this mem- 

 brane breaks up the nuclear bodies are disseminated 

 through the surrounding protoplasm, and later play 

 the part of nuclei. 



The multiplication of the nucleus is, however, 

 often carried out in the simple manner of binary sub- 

 division ; and a karyokinetic division has been 

 observed by Lister in the nucleus of Pohjstoniella 

 crisp a. 



Solid particles of a more or less granular structure 

 are often present in the protoplasm ; they are capable 

 of being stained like the nucleus by various reagents. 

 They are referred to as nutritive particles, and 

 probably represent various stages in the assimilation 

 of food material. 



Pieproductioii and Dimorpliisni. — The production 

 of young in the shells of Foraminifera has long been 

 known, for they were observed as long ago as 1847 

 by Gervais, who noticed a brood of young shells, 

 each consisting of a single large chamber, and 

 numbering about one hundred, grouped together in 

 the orifice of a species of Miliolina which had been 



