118 ELEVENTH REPORT. 



THE EARLY DEVELOPMENT OF NEVROFIBRILLAE IN RANA 



AND AMBLYSTOMA. 



H. M. MacCurdy. 



f (Abstract) 



The observations of Harrison on the hving developing nerve cell in the 

 larvae of Rana, and of Held on the development of neiirofibrillae in Am- 

 phibian and other emliryos, suggest the possil^ility of correlating the develop- 

 ment of structure and function in the earty stages of the growth of the indi- 

 vidual. Held has described neurofibrillae in the neurblasts of the larva^ 

 of Rana fusca 5.5 mm in length, in axolotl larvse 5 mm in length, in 3 and 

 4 days old duck embryos and in later stages in trout em1:)ryos. 



In the study of the developing nerve cells in embryos of Rana pipiens. 

 H. cantabrigensis, and Amblystoma, 1 have found neurofibrillae in the 

 neuroblasts as early as it is possible to distinguish the outgrowing nerve 

 fiber. 



In embryos of R. cantabrigensis fibrillae are present at the end of the 

 second or the third day in larvse scarcely 3 mm. in length. In R. pipiens they 

 appear later, in larvae 4 mm. in length, and in Amblystoma* they arise some- 

 what later still since the development is slower in the latter form. So far as 

 it has been possible to make out, neurofibrillae first appear in the ventro- 

 lateral portion of the neural tube giving rise to the mid brain. Fibers bearing 

 fibrillae extend ventrally connecting the two sides, and they also extend 

 posteriorly along the ventral surface of tlie two sides of the developing neural 

 tube with no direct fiber connection at first between the two sides ventrally 

 so far as can be seen. Neurofibrillae are also present in the first fillers to be 

 seen in the developing optic nerve, in which they can be seen extending to 

 the retinal elements as soon as the latter are sufficiently differentiated to be 

 recognized. 



Neurofibrillae, therefore, are present in the nerve elements ]:)efore the 

 latter assume their regular function, and it is reasonal^le to assign to the 

 fibrillae some part in the functioning of the nerve elements when normal 

 body movements begin or when the embryos first show a response to tactile 

 stimuli. 



The order of the origin and development of the nerve fillers tracts and 

 neurofibrillae is in general accord with the origin and development of the 

 first observable normal body movements of the embryos, and precedes those 

 movements in point of time. The same may^ be said of the first responses 

 to the tactile stimuli as far as they have l^een observed. The presence of 

 conduction paths determines the reactions. 



*A. jeffersoniamem. 



