390 E. V. COWDRY 



first to claim that they are transformed into neurofibrils. He 

 brings forward the following generalization ('08, p. 845): that, 

 with the specialization of the embryo into different organs ^nd 

 tissues, primitively similar cells assume special functions which 

 find expression in characteristic structures or differentiations. 

 All these products, no matter how heterogeneous they may be, 

 arise through the metamorphosis of one and the same elemen- 

 tary plasma-constituent, the chondriosomes (mitochondria) . Thus 

 the different filamentous formations, such as the various fibrillar 

 structures of epithelial cells, the protoplasmic filaments of epi- 

 dermal cells, the fibrils of smooth and striated muscle, the neuro- 

 fibrils, neuroglia threads and connective tissue fibrillae are, accord- 

 ing to his conception, to be classified as products of chondriosomes. 



Dr. Bensley pointed out to me certain facts which are incon- 

 sistent with this hypothesis of the transformation of mitochon- 

 dria into neurofibrils. The far-reaching biological significance of 

 this generalization of Meves, relating, as it does, to the funda- 

 mental properties of protoplasm; and the pressing need for further 

 light upon the nature of the cytoplasmic constituents of ani- 

 mal cells, from the standpoint of both ontogenesis and phylo- 

 genesis, in order that investigations dealing with changes in cells 

 under different functional conditions may be based on a secure 

 foundation, have induced me to undertake this investigation. 



I therefore decided to follow up my previous paper ('12 a) in 

 which I determined the morphological independence of the mito- 

 chondria, chromidial substance, canalicular apparatus and neu- 

 rofibrils in adult spinal ganglion cells of the pigeon, by further 

 investigations the object of .which would be (1) to determine as 

 far as possible, the origin of the neurofibrils, chromidial sub- 

 stance and canalicular apparatus; (2) to study the morpholog- 

 ical relations of these structures to each other in the course of 

 development; and (3) to elucidate their functional significance. 

 I have attempted throughout to give a full and accurate descrip- 

 tion of my findings, to state concisely their bearing upon the 

 problems involved and to avoid transgressions from the realm of 

 fact into the domain of theory, because we are at present ham- 

 pered by a dearth of facts and a multitude of theories. 



