THE FORAMINIFERA 71 



nucleus is, as Schulze pointed out (64, a), usually found in or 

 near the chamber which is numerically in the middle of the series. 



In the cells of growing vegetable tissues the nucleus moves towards that 

 part of the cell at which growth is most actively proceeding. 1 Thus in a 

 growing root-hair the nucleus is found near the tip ; in a young stellate 

 hair, it lies at the point of junction of the rays. Its movement towards 

 the regions of activity results, we must suppose, from a certain force 

 impelling it in that direction, and its position when at rest is at the point 

 where the impelling forces, resulting from the activities of the protoplasm 

 in different parts of the cell, are in equilibrium. 



In the forms of Foraminifera in which the nucleus is single it 

 appears that its position is likewise dependent on the disposition of the 

 protoplasm. Thus in the megalospheric forms of Cycloclypeus and Orbi- 

 tolites complanata the nucleus is found in or near the central chamber, 

 where, owing to the cyclical growth in these genera, the attractions, due 

 to activity at the periphery, are in equilibrium. In the forms with 

 spiral arrangement the nucleus moves on through the series of chambers 

 as growth proceeds. In Polystomella, however, the nucleus of the 

 megalospheric form always lags some distance behind the point at which, 

 judging from the disposition of the bulk of the protoplasm, we should 

 expect the attractive forces to be in equilibrium. 



At the earliest stage at which it has been recognised the nucleus 

 appears to be a homogeneous body. As it grows, round nucleoli 

 make their appearance, and these are comparatively large in young 

 specimens, and decrease in size while they increase in numbers as 

 growth proceeds. 



Sections through the nucleus of specimens fairly advanced in 

 growth show a well-defined nuclear wall, a reticulum with finer 

 or coarser meshes occupying the interior, and rounded nucleoli at 

 the nodal points of the reticulum. Minute granules may often be 

 detected in the strands of the reticulum. 



It appears that throughout the vegetative phase of the megalo- 

 spheric form small fragments are separated off from the nucleus, 

 and they may often be seen as irregular bodies, sometimes con- 

 taining nucleoli, lying in the neighbourhood of the nucleus, or in 

 the chambers through which it has passed in its passage onwards 

 from the megalosphere. 



Towards the end of the vegetative phase of the life-history of 

 the megalospheric form the nucleus loses its regular outline and 

 its power of receiving stains, and finally disappears. In such 

 specimens it may often be observed that additional passages have 

 been opened up, by the dissolving action of the protoplasm on 

 the shell substance, between adjoining chambers of inner and 

 outer convolutions, so that the inner chambers are placed in 



1 Cp. Haberlandt's researches, quoted by 0. Hertwig, Die Celle und die Gewebe 

 i. p. 259. 



