392 E. V. COWDRY 



are blackened by silver impregnation after Cajal. He adds that 

 the completed neurofibrils (in the later stages of ontogenesis) 

 cannot be stained by mitochondrial methods in the same way that 

 the forerunners of the neurofibrils in the cells of the medullary 

 tube, which stain by silver impregnation from the beginning of 

 the third day, may be so demonstrated. He believes that there 

 is a period in development when the neurofibrils may be stained 

 by mitochondrial methods and also through silver impregnation. 



Duesberg ('10, p. 612) refers to the researches of Meves and 

 Hoven regarding the development of neurofibrils from mito- 

 chondria and remarks that the number of chondriosomes di- 

 minishes with the increase in the age of the embryo until in the 

 adult nerve fiber none remain stainable by Benda's method. 

 Meves, in a recent paper ('10 a, p. 655), apparently confirms this 

 observation for he concludes that no chondriosomes remain, as 

 such, in adult spinal ganglion cells. 



Hoven ('10) has furnished the most detailed observations in 

 support of the mitochondrial origin of neurofibrils. He studied 

 the formation of neurofibrils in the cells of the neural tube and 

 spinal ganglia of chick embryos by the application of the Benda 

 method and of Cajal's silver impregnation method. He found 

 that the morphology and cytoplasmic arrangement of the chon- 

 driokontes, as demonstrated by Benda's method, bears a very 

 striking resemblance to the appearance of the earliest neurofi- 

 brils demonstrable by silver impregnation in cells of the same stage 

 of development. The chondriosomes at this period form a re- 

 ticulum of undulating filaments (p. 475). Furthermore, in latei- 

 stages the chondriokontes decrease in number as the neurofibrils 

 increase in amount, and he asks the question if the chondrio- 

 kontes do not give rise to the neurofibrils what becomes of them? 

 He believes that the few which do persist in the adult nerve cell 

 correspond to the internal reticular apparatus of Golgi, the Bin- 

 nennetz of Kopsch, etc. As corroborative evidence he draws a 

 close analogy between the formation of myofibrils, as indicated by 

 Duesberg ('09 and '10), the transformation of chondriosomes 

 into connective tissue fibrils (Meves '10) and* the formation of 

 neurofibrils from chondriosomes. 



