166 bulletin: museum of compakative zoology. 



In his study of tlie development of the cranial nerves of Ammocoetes, 

 von Kupffer ('9X) assigned to the nerve he believed homologous with 

 the oculomotor of higher vertebrates both dorsal and ventral roots and 

 spinal as well as sympathetic ganglia. In a later paper (von Kupffer, '95) 

 he states that the oculomotor in Ammocoetes appears to be a ventral 

 nerve with which is related dorsally the anterior half of the first trigemi- 

 nal ganglion. 



The third nerve and the ciliary ganglion in embryos of Amia calva are 

 described by Allis ('97). This writer has, however, no positive informa- 

 tion to offer as to the early stages of their development. 



Hoffmann ('97) states that the oculomotor, when first detected in 

 Acanthias vulgaris, appears as a fibrous ventral root. At this time 

 there is no ganglion at the proximal end of the nerve. His observa- 

 tions on the abducens confirm those of Marshall and van Wijhe. 



Chiarugi ('97) declares, in opposition to Mitrophanow, that the third 

 nerve in selachians grows centrifugally from the base of the mid-brain. 



By the use of his modification of the vom Eath method, Neal ('98) 

 demonstrated in so convincing a manner the neuroblasts of the oculo- 

 motor and their processes in Squalus acanthias that he removed all 

 doubt as to the origin of the nerve from the ventral wall of the mid- 

 brain. The neuroblasts showed the characteristics of those described 

 by His in the spinal cord, and their darkly staining processes could be 

 followed partly into the mesenchyme, where they were grouped to form 

 the nerve trunk, and partly in a posterior directicm within and parallel 

 to the medullary wall, where they took part in the formation of the 

 ventral fibre tract. The nerve growing out in this fashion from the 

 mid-brain exhibits many nuclei lying peripherally along its fibres. It 

 soon connects with the cells of the mesocephalic ganglion. Whereas 

 the nerve is several cells in thickness near the ganglion, its calibre 

 grows less toward the brain wall, a condition which, if one were unac- 

 quainted with its earlier history, might lead to the supposition that 

 the growth of the nerve takes place from the ganglion toward the bniin. 

 Cells were observed migrating out from the mesocephalic ganglion 

 and adhering closely to the oculomotor fibres. The fate of these cells 

 was not determined, nor was the develojiment of the ciliary ganglion 

 followed. No entirely satisfactory evidence of migration of medullary 

 elements was observed. 



The abducent nerve was found by Neal to arise in the form of a 

 slender bundle of neuraxons from neuroblasts situated in the ventral 

 horn of the medulla. The number of its roots increases during devel- 



