ON THE LIFE-HISTORY OF THE FOKAMINIFERA. 135 



gradually increase in size as they are situated further along the 

 series. Thus, in one specimen, the innermost nucleus measures 

 30 X 20 n, and the outermost 48 x 38 /t. 



Structure of the Nuclei. — In sections the nuclei appear to 

 consist of a homogeneous substance which stains moderately 

 deeply with picro-carmine, with deeply stained nucleoli, round 

 or oval, embedded in it. The nucleoli vary much in size and 

 number, and when large may contain round vacuolar spaces 

 with clear unstained contents (figs. 8 and 9). The large nuclei 

 contain larger nucleoli than the small ones. Externally the 

 homogeneous inter-nucleolar substance does not appear to be 

 limited by a membrane or wall of any kind, but terminates 

 sharply against the coarse reticulum of the surrounding proto- 

 plasm. 



Division of the Nuclei. — Very often the nuclei are disposed 

 in pairs in the protoplasm, and in some cases the opposed sur- 

 faces are flat arid corresponding, as though marking a plane of 

 division (figs. 9 and 10). 



In a specimen of one of the microspheric individuals which 

 was cut into sections, a nucleus in process of division is seen 

 (fig. 11, a-c) in three consecutive sections. It so happens that 

 the plane of the sections passes nearly at right angles to the 

 plane of division of the nucleus. In the first section both 

 divisions of the nucleus (which I will distinguish as right and 

 left) are seen united by a constricted portion, and the right 

 division appears larger than the left. In the next section a 

 similar appearance is presented, but now the left is larger than 

 the right. In the third section the left half alone appears. 

 The nucleoli and the inter-nucleolar substance present exactly 

 the same appearance as in nuclei which are not undergoing 

 division. 



It may, I think, be taken as a fact that the nuclei of the 

 microspheric form increase in number during the earlier stages 

 of growth by simple division. 



Dispersal of Nuclear Substance. — Besides the round or oval 

 nuclei, there are very generally present in the protoplasm irre- 

 gular strands of red-stained substance. These may be small 



