Loxogenes arcanum Nickerson. 285 



Figs. 13 and 14 show two cells in a later stage of this process. 

 The cell has undergone a considerable increase of size and the cj'to- 

 plasm has segregated itself away from the stored material and forms 

 a cap at its deeper end. resting upon the rest of the material. A 

 distinct wall can be seen. The true cytoplasm of the cell is distinctly 

 though faintly tinged by the iiDn-haematoxylin. A nucleus occupies 

 its centre. This nucleus agrees in size and structure with that of 

 the resting cells in the bladder worm sections. One notable feature, 

 in these cells as well as in other stages, is the tendency they show 

 to become enlarged distally and to taper toward the body wall. 

 They may retain a point of contact with the wall as in 12 and 14. 



The segregation of the cytoplasm from the secondary material 

 of the cell, recalls the fat cell of vertebrates, and indicates that in 

 the living cell, the substance in a fluid which compresses the cyto- 

 plasm in a way analogous with the adipose cell. It cannot however 

 be a fluid as thin as oil since the cells do not assume a spherical 

 outline. It is evidently more gelatinous and denser. 



Two other types of cells, in which this activity was going on, 

 are shown in Figs. 15 and 16. For reasons which will appear in a 

 moment, I have concluded that 15 is earlier and that 16 represents 

 the last stage in the series. The enormous size which this cell has 

 attained is at once seen on comparing it with the others and be- 

 comes especially striking when this cell is compared with the resting 

 cells of Fig. 11. The cap of cytoplasm is still recognizable on the 

 inner aspect of the mass, it has not increased greatly in volume, 

 has the same reaction to the stain and contains a nucleus of the 

 same size and form as before. The chief change which has taken 

 place in this cell has been in the stored material; this has increased 

 greatly in amount. It is also seen to be vacuolated in places, seven 

 such vaculoes are seen in the section. A similar vacuole is seen 

 in Fig. 14. At its outer end this cell is very irregular owing to 

 the presence of several processes reaching out toward the surface 

 and leaving open places between them. This tendences to reach out 

 toward the cuticula is seen in all the sub-cuticular cells. At its 

 upper end (in the figure) the boundary of the cell becomes uncertain 

 and its substance encloses several nuclei some of which are sur- 

 rounded by radial threads of blue-stained substance. The cell shown 

 in Fig. 15 ditfers from the others, which have been described in 

 respect to the four cells which lie at its outer end. This cell has 

 the usual segregated and compressed cytoplasmic region with its 



19* 



