256 FISH. [Vol. X. 



Protopteriis . was demonstrated in the Desmognathus. The 

 specimens showed what appeared to be a slight thickening 

 of the pia between the dorsal and ventral roots ; while in 

 a small larva of 17 mm. there appeared a cord, Fig. 18, 

 similar in size but nearer the ventral than dorsal root, con- 

 necting the ventro-lateral angle of the myel with the dura 

 or ganglion, and it seems quite likely that this cord which has 

 quite a semblance to a lateral root is functionally a ligamentum 

 dentatum excessively developed in order to support the myel, 

 which as yet does not nearly fill up the spinal canal. When 

 the canal becomes more completely filled the ligament becomes 

 reduced to a much smaller size and loses its peripheral attach- 

 ment. Figs. 37, 38, 54, 57. The ventral root leaves the myel 

 not far from the ventral furrow, the dorsal root enters at about 

 the dorso-lateral angle of the myel. 



In transection the lateral diameter of the myel is greater 

 than the dorso-ventral ; the myelocoele is small but distinct and 

 shows no traces of cilia, as indeed did none of the brain cavities. 

 Numerous cells, from five to seven layers deep, surround the 

 cavity, forming an entocinerea ; this ental column of cinerea is 

 preserved throughout the whole neuraxis and is in marked 

 contrast to the condition found in mammals where the brain 

 is characterized by a strong development of ectocinerea. Of 

 these layers of cells those most dorsal approach most nearly to 

 the periphery. The dorsal and ventral horns are quite well 

 marked ; the latter are relatively broad and do not extend as 

 near the surface as do the dorsal. The cells are not confined 

 to the cinerea, many are found scattered irregularly through 

 the alba. There is, perhaps, some appearance of grouping at 

 the ventro-lateral angles of the cord and this may possibly have 

 some significance in connection with the close proximity of the 

 ventral nerve root. 



Klaussner (20) differentiates the cinerea of the myel into 

 zones, the most ental of which is composed of epithelial cells 

 from five to six cells deep ; the middle zone shows a distinct 

 fibrous structure and consists of fine fiber tracts and networks; 

 the ectal zone lies next to the alba and is characterized by the 

 appearance of what he considers true nerve cells. 



