352 ABSTRACTS OF PAPERS. [VOL. II. 



The pharynx may be formed in a region of the piece at some 

 distance from the cut surface. Head, lateral, and tail areas are 

 differentiated only at a cut surface. 



The reproductive organs are not regenerated. Instead, they 

 disappear from a small piece isolated from a sexually mature 

 worm. The tail cut from a planarian in which the reproductive 

 organs are developing will give rise to regenerative forces which 

 overpower the forces giving rise to the sexual organs. Regen- 

 eration is equally rapid in sexually mature and in sexually 

 immature worms. 



In regeneration in this animal the tissues seem to be spe- 

 cific, except that the new musculature probably comes from 

 parenchyma cells. 



A full account of the Physiology of Regeneration in these 

 animals is given in the American Journal cf Physiology, 

 Vol. V (1901), p. i. 



XVIII. THE HISTOGENESIS OF THE PERIPHERAL 

 NERVOUS SYSTEM IN SALMO SALAR. 1 



ROSS GRANVILLE HARRISON. 



CELLS provided with pseudopodia-like processes wander out 

 singly from the dorsal surface of the medullary cord, and 

 collect together between the myotomes and the cord into 

 small groups, the spinal ganglia. Here the cells remain for 

 some time undifferentiated, but are transformed later into 

 bipolar cells, of which the centripetal processes grow into 

 the side of the medullary cord to form the dorsal roots. 



Neuroblasts may be distinguished at an early stage as round 

 or polyhedral cells, lying in the outer zone of the cord. At 

 this period the cord is made up chiefly of epithelial cells, the 

 forerunner of the ependyma. These cells are still undifferen- 

 tiated, no specialized " Ra ndschleier " being present. As the 

 axones grow out from the neuroblasts, they bore their way 



1 A full account of this work is published in the Arc/tiv fiir mikroskopische 

 Anafomit-, January, 1901. 



