CoGHiLL, Structure of the Nerve Cell. 183 



toplasmic processes of the cells of the spinal cord of the rabbit and cat. 

 Besides the ordinary club-shaped gemmules there are others, in the 

 animal just born, in the form of fine filaments or spines which often 

 arise from a small conical projection of the dendrite. In the middle of 

 this filament may sometimes occur a small thickening. The processes 

 of the posterior horn cells have the same type of gemmules but have 

 tliem in much larger numbers. 



In a rabbit two weeks old the processes have become more regu- 

 lar in oudine. This change appears only in the basal part of the den- 

 drites and advances with age towards the periphery. The filamentous 

 gemmules do not appear at this stage all along the dendrites as they 

 did in the rabbit one day old, but occur only in the more distal, irregu- 

 lar part of the process. In a rabbit one month old they are found 

 oidy on the extreme terminal branches of the dendrite. In cats from 

 birth to one month old the same mode of development is followed. 

 But in kittens two months old Geier found no typical filamentous 

 gemmules upon the anterior horn cells. In place of them were similar 

 processes of much larger size. This, together with the fact that in an 

 animal three days old the filamentous gemmules are two or three times 

 larger than they are at birth, indicates that some at least of these gem- 

 mules grow into dendritic branches. Geier believes that all such gem- 

 mules of the young cells are dendrites in the process of development. 



This peculiar type of gemmule is not found upon the posterior 

 horn cells, but the more complex forms are very abundant on the 

 dendrites and occur also on the cell body. Geier concludes that the 

 gemmules are relatively rare upon the anterior horn cells and of a con- 

 stant form while they are exceedingly numerous and variable in form 

 upon the cells of the posterior horn. Their absence in any case is as- 

 sociated with the moniliform condition of the dendrites. 



Paton ('00) interprets the gemmules as artifacts which mark the 

 points at which the fibrillae of the pericellular net enter the cell or come 

 in contact with it. He asserts that the appearance of the gemmules 

 upon the cortical cells of the embryo is synchronous with the appear- 

 ance of neurofibrils. 



That the gemmules mark the point of continuity between the in- 

 tracellular and the pericellular fibrils is denied by Hatai. He de- 

 monstrates the neurosomic net within the gemmule and the neurosomic 

 nature of the axone terminals which compose this pericellular net. 

 But, while the two fibril systems come into intimate touch with each 

 other, especially at the gemmules, they differ sufficiently in structure 



