300 'Journal of Comparative Neurology and Psychology. 



the lines forming the reticulations cross. The nucleus remains 

 globular with a clear outline, in fact is not distinguishable from 

 that of the resting cell. The two things most striking about these 

 modified cells are their great increase in height, and the appearance 

 of so much clear space at the distal side of the nucleus. 



The apical structures of epithelial cells according to Vignon 

 ('oi) take no part in the functional activity of the cell. In case ol 

 the extrusion of droplets, they may be pierced, but there is no 

 change in their structure during the process. In the case of the 

 rabbit, where there are fatty droplets, which we consider a secre- 

 tion of secondary importance, we can find no evidence of any 

 change in the marginal zone of the cell. The globules evidently 

 pass out without anything more than rupturing the plateau, and 

 this soon reunites. In the case of the typical secretion, however, 

 the evidence seems to be that the marginal zone of the cell is 



b c 





k' '-'^--a 



Fig. t). Cells from a dog's plexus after ether anaesthesia. Secretory changes are to be noted 

 Magnification X 1800. a, Marginal zone; h clear areas toward apes; c, fat droplet. 



modified. A comparison of Fig. 4 with Fig. 8, both from the 

 rabbit, will show that the marginal zone of the resting cell has 

 been transformed into a simple, thin, granular wall. We do not 

 believe that the apical wall of the cell disappears during the secre- 

 tion, but it is evidently considerably modified. 



Fig. 9 shows secreting cells from a dog subjected to ether anaes- 

 thesia for 30 minutes. Fatty droplets have not been found in the 

 normal epithelium of the dog's plexus, but it is seen that they 

 appear after use of ether. The third cell from the left shows a 

 large droplet which has compressed the nucleus. As in the pre- 

 ceding case, the cells are twice as high, the outer part of the cell 

 contains many clear areas, and the marginal zone has been trans- 

 formed into a simple granular line. 



The mechanism of secretion, not only in the choroid plexus, but 

 in general, has been a much discussed subject. In this connec- 



