THE MITOCHONDRIAL CONSTITUENTS OF PROTOPLAglVt. 125 



transverse striation, but the longitudinal striation is very marked. It is difficult 

 to analyze. Apparently several factors enter into it. In the first place, there 

 are the fibers of Mliller, which do not belong to the cell itself. The exoplasmic 

 prolongations of the membrana liniitans externa give a striated appearance. The 

 so-called baskets ("corbeilles") also contribute to it. These are supportive. The 

 cell-membrane itself seems, according to the best accounts, to be striated. Mawas 

 (19106, p. 117) emj^hasizes, in the rabbit and in man, a striation which is intra- 

 cytoplasmic and wliich is due to the pecuhar arrangement of the mitochondria in 

 a peripheral sheet just beneath the cell-membrane. This, however, Leplat (1913, 

 p. 220) failed to observe in birds. Leboucq (1909, ]). 594) gives a detailed descrip- 

 tion of a system of intracytoplasmic filaments arising near the centrosome at the 

 base of the external segment, at first spreading out in the inner segment to form 

 the "ellipsoid" or "Fadenapparat," then condensing into a single filament, in 

 the rods, and into a bundle of three or four filaments in the cones and running 

 toward the nucleus. The neurofibrils are also to be reckoned with in connection 

 with this longitudinal striation; little is known for certain about them. Small 

 droplets of oil, "Olkligeln," occur in this inner segment in the early stages of devel- 

 opment and may persist in the fully differentiated state. Small quantities of pig- 

 ment are occasionally observed. Nothing is known of the Golgi apparatus in the 

 rods and cones in the adult condition, though Cajal (1915, p. 21) has described and 

 figured them in the early stages of development. Now that we have an idea of 

 the elements, we can proceed with the problem at hand. It is the envelope of the 

 external segment of the rods and of the cones that is said to be formed by a trans- 

 formation of mitochondria. 



Leboucq (1909, p. 593) was the first to advance this view on the basis of his 

 observation that it stained intensely violet (Uke mitochondria) by the Benda 

 method of coloration, but his paper deals more with the centrosomes and their 

 transformations than with the mitochondria and is merely suggestive. 



Mawas (19106, p. 114) studied the mitochondria in the fully developed retinae 

 of a number of vertebrates, including man (1910c, p. 113). He did not use any 

 embryos. He calls attention to the fact that the external segment stains intensely 

 with iron hematoxylin, hke the myelin of peripheral nerves, and blackens with osmic 

 acid, like fat (Ranvier). In addition, he confirms Leboucq's and Magitot's observa- 

 tions that it stains with mitochondrial dyes. It is soluble in alcohol and xylol. 

 These are, he says, the reactions of mitochondria, and he therefore looks upon the 

 external segment of the rods and of the cones as an example of diffuse mitochondrial 

 material present in protoplasm without any structural differentiation whatever. 



Leplat (1913, p. 219), extending some already published work, attacked the 

 same problem in the developing chick with mitochondrial methods with a view 

 to determining exactly the part played by the mitochondria. He described the 

 heaping-up of mitochondria (first around the base of the axial filament in the 

 external segment) and their subsequent extension along its whole length. These, 

 he believes, form the envelope (p. 218) and he attempts to draw a close analogy 

 between this process and the grouping of mitochondria around the axial filament 



