ON THE LIFE-HISTORY OF THE FORAMINIFERA. 141 



number of chambers containing protoplasm of the specimens whose nuclei are 

 measured. 



The figure placed by each dot shows the number of specimens having a 

 given number of chambers, the average diameter of whose nuclei is here given. 



The upper curve refers to specimens preserved fresh from the sea, the lower 

 to specimens kept for three months with scanty food supply. 



The curves overlap at one point, but do not cross. 



the curves is sufficient to show the marked diminution in the 

 size of the nucleus under the conditions in which the animals 

 were kept. 



Structure of the Nucleus. — In a section through the nucleus, 

 which has been stained in picro-carmine, and in hsematoxylin 

 (fig. 14) or methylene blue, so as to give a contrast in colour 

 between the nucleus and the surrounding protoplasm, the out- 

 line of the nucleus is generally sharp for the greater part of the 

 periphery. It is not unfiequently the case, however, that there 

 are regions where the sharpness of the separation is lost. This 

 appearance I believe to be due to the fact that the plane of the 

 section here cuts the nucleus obliquely. 



Although, as F. E. ScHULZE states, the nucleus often ap- 

 pears to be surrounded by a definite membrane when seen in the 

 whole specimen, and in sections has a well-marked limit (figs. 

 14 and 16), I have failed, in examining sections, to see a clear 

 indication of a nuclear wall which is distinct from the proto- 

 plasm on the one hand, and the contents of the nucleus on the 

 other. 



Three elements are to be distinguished in the nucleus : the 

 nucleoli, the reticulum, and the intermediate substance. 



The nucleoli appear to be invested by the substance which 

 forms the reticulum, and the strands of the latter spring from 

 this investment (figs. 14 and 16). They are round or oval 

 bodies, staining readily with picro-carmine. They present great 

 differences in different individuals. Their size in a given nucleus 

 may be nearly uniform, or it may vary widely. If large, they 

 generally contain one or more cavities (figs. 14, 18, &c.). Some- 

 times the nucleoli are compound morula like masses, whose 

 appearance suggests that a large nucleolus is breaking up into 

 a number of small ones (figs. 17 to 19), and frequently their dis- 



VOL. VI. 14 



