158 



and discussed at length the relation of the cells of the cerebellum to 

 the PuRKiN.JE cells of higher forms (p. 22, 57). I stated that "the 

 Purkinje cells have not yet been differentiated", but showed that the 

 cells in the cerebellum of Petromyzon are similar to those in the 

 tuberculum acusticum. Further than this, I traced the steps in the 

 evolution of Purkinje cells in fishes. I beheve that I have furnished 

 (1901, 1902, 1906, 1909) a knowledge of "die Uebergangsstadien von 

 dem Zustand der Kleinhirnelemente, wie wir sie bei den Cyclostomen 

 finden, zu den Formen bei höhereu Tieren" which Tretjakoff says 

 are not known. 



P. 691. The author states that I regard the mitral and stellate 

 cells in the tectum as belonging to the "amacrine cells". I understand 

 the author to mean by amacrine cells, neurones which are not provided 

 with true axones. I have not recognized any such cells in the brain 

 of Petromyzon and have described the axones of all the types of cells 

 in the tectum. 



In various places Tretjakoff's interpretation of the structure of 

 the Petromyzon brain would have been greatly improved if he had 

 understood and made use of the principles of functional morphology 

 which have been developed in the last fifteen years. The work of 

 numerous authors has shown that in fishes, amphibians, mammals and 

 man the vagus nerve contains fibers which are distributed to the skin 

 and which enter the tractus spinalis trigemini centrally. These cuta- 

 neous fibers are to be sharply distinguished from those which are 

 distributed to the mucosa. Instead of recognizing this, Tretjakoff 

 (p. 658) is led to the conclusion that the vagal rootlets which enter 

 the spinal trigeminal tract do not belong properly to the vagus but 

 represent the first spinal dorsal root which has secondarily united with 

 the vagus during the ontogeny. No ground is given for this extreme 

 view. It is necessary to recognize that the true vagus nerve characte- 

 ristically contains a cutaneous component. 



A much more serious criticism is to be made upon the author's 

 study of the Nn. vagus, glossopharyngeus and facialis. Judging from 

 the descriptions and figures it seems to me very probable that Tret- 

 jakoff has not seen the visceral sensory components of 

 these nerves at all. The visceral sensory component is known 

 also by the name communis component because the fibers enter into 

 the formation of the fasciculus communis in the brain (Osborn, Strong). 

 The fibers of this component are distributed peripherally to the mu- 

 cosa lining the mouth, pharynx and intestine. They also supply taste 

 buds wherever they are found. (Schluß folgt.) 



