ON THE LIFE-HISTORY OF THE FORAMINIFEEA. 149 



Rhumbler shows that the large solitary nucleus of this 

 species is gradually altered during its growth. The Binnen- 

 korper, the nucleoli of other authors, which in young specimens 

 are few, large and frequently compound, after increasing in 

 numbers at first, become in the later stages fewer or disappear 

 altogether. Meanwhile chromatin granules appear in the 

 nucleus, and increase in numbers, becoming embedded in linin 

 fibres. In the course of development, the substance between 

 the Binnenkorper, which is at first homogeneous, becomes 

 vacuolated and then formed into a well-marked reticulum 

 (Wabenwerk) which appears first at the centre, and gradually 

 extends to the periphery of the nucleus. Finally, the nuclear 

 wall, which has been very distinct in previous stages, disappears, 

 and the linin fibres with the chromatin grains are dispersed in 

 the protoplasm. 



It is suggested that the last stage of this process is prepara- 

 tory to reproduction. 



There are clearly several points of resemblance between the 

 nuclear changes of Saccammina and those of the megalospheric 

 form of Polystomella. I find, on referring to my specimens, 

 that minute granules are frequently present in the reticulum, 

 which may very possibly be grains of chromatin, though they 

 are not seen so distinctly as in the very large nuclei described 

 by Rhumbler. On the other hand, the nucleoli of Polystomella 

 stain more readily with picro-carmine, and appear to retain 

 their large size for a longer period than those of Saccammina. 



Saccammina belongs to the family Astrorhizidm, and builds 

 a test which is generally single chambered, and is composed of 

 foreign particles cemented together. This, as Rhumbler 

 clearly shows, is expanded to accommodate the growth of the 

 contained protoplasm. Hence, the evidence of dimorphism, 

 which is afforded by the first formed chambers of the shell in 

 many multiloculate Foraminifera, cannot be present here. But 

 it does not appear that there is evidence of dimorphism to be 

 derived from the nuclei, whose condition in Polystomella and in 

 the species described below, is so different in the two forms. 

 Out of the 286 specimens examined by Rhumbler, a single 



