ON THE LIFE-HISTORY OF THE FORAMINIFERA. 147 



probable that they are so derived from a single nucleus. After 

 maintaining their rounded form for a certain time, the nuclei 

 give off portions of their substance, which become dispersed in 

 the surrounding protoplasm. 



Of the further history of the microspheric form of this 

 species my preparations yield no evidence*. 



The Megalospheric form, during the greater part — the vege- 

 tative period, — of its life, has a single large nucleus, which 

 grows in size with the growth of the protoplasm, and passes on 

 from chamber to chamber ; moving towards the centre of the 

 bulk of the protoplasm, though lagging some distance short of 

 it. It contains a nuclear reticulum, nucleoli, which occupy the 

 nodes of the reticulum, and a substance occupying the meshes. 

 The nucleoli appear to increase in number and diminish in size 

 with the advance of the organism. There is reason to believe 

 that, as the nucleus moves on through the chambers, portions 

 of its substance are given off into the protoplasm. It appears 

 that this may occur either by the separation of considerable 

 portions (figs. 24 and 25), sometimes containing several nucleoli, 

 which lie strewn along the track it has followed, or by the 

 dispersal of minute fragments into the surrounding protoplasm, 

 causing a flush in the neighbourhood of the nucleus in the 

 stained specimens (fig. 23). 



What is the fate of the large nucleus ? It might be 

 supposed that it divides up by binary fission, and so gives rise 

 to the small nuclei which are found later. As stated above, I 

 have met with twenty-one cases in which more than one large 

 nucleus is present, and in two there are as many as seven nuclei. 

 Do these represent stages at the beginning of the process ? 



If there are twenty-one cases in which binary fission has 



begun and the segments into which the nucleus has divided are 



still large and few in number, the cases in which, by this 



process, many nuclei of smaller size have been produced, ought 



to be abundant. The fact is, that amongst the 1760 examples 



of the megalospheric form which have been examined (up to 



* The mode of reproduction of the microspheric form is briefly described in 

 Postscript 2. 



