MiTROPHANOW, Development of Nervous Elements. 167 



distingushes them from the mesodermic elements ; the histolog- 

 ical difference between the embryonic elements in the chick is 

 less considerable. All our knowledge of the development of 

 the nerves obliges us to think that the ganglionic outgrowths 

 preserve their individuality till the formation of the nerves, 

 though by the ordinary methods, this is inconspicuous, as we 

 see it, for example, in the region of the trigemini. We know 

 from the study of the Selachia that the embryonic group of this 

 nerve (the first outgrowth ot Goronowitsch) presents compli- 

 cated and well determined modifications; probably identical 

 facts may occur in the chick. 



If the nerve (or the ganglion) is formed at the point where 

 the ganglionic outgrowth was at first clearly seen, it is natural 

 to think that the elements of the latter have been used for the 

 formation of the nerve (or ganglion) and not the elements of 

 the mesoderm, which is formed from the same outgrowth. 

 The late formation of the mesodermic elements (mesenchyme) 

 of vertebrates from the ectoderm is a point to which much 

 study must yet be given, and it awaits further elucidation. 

 That the embryonic elements which form the germ of the nerve 

 are exclusively used for the tissue enveloping the nerve is also 

 a question to be developed. A part of these elements which 

 have in every case been formed through the ganglionic out- 

 growths, or as I have presented it, through the embryonic 

 groups, is certainly used for the formation of the ganglion cells ; 

 others perhaps form the sheath of Schwann and, through its 

 agency, the medullary sheath, and the purely mesodermic cells, 

 penetrating later into the nervous germ (fundament), are used 

 for the formation of the connective tissue which combines the 

 nervous elements into a single whole.' 



1 The editor has in a few instances taken some liberties with the phrase- 

 ology in the interests of the conventional English idiom, but trusts that he has 

 in no case departed from the meaning of the learned author's original. It is to 

 be regretted that the typography of an American printing office make it impos- 

 sible to give the titles of the Russian papers quoted in the course of this 

 article. The editor ventures to express his gratification in the substantial 

 identity of results attained by the author and those reached by other methods 

 by himself. 



