The Nervous System of Amblystoma. 437 



Definition of Terms 



Since, as has been shown in the preceding review, authors 

 have not agreed upon tferms and since many of the old terms 

 have proved to be misleading it seems necessary to adopt a 

 definite system of nomenclature. The terms used in this paper 

 are as far as possible those of earlier writers. Where a choice 

 between two old terms was made, or where a new term was 

 chosen, it was done with the purpose of showing the position 

 and relations of the structure involved without suggesting 

 doubtful homologies. 



In the first place the common term, primitive groove, has been 

 avoided altogether. This word has been used in various senses 

 by different authors, and furthermore it suggests a doubtful 

 homology which it is not the purpose of this paper to discuss. 

 The groove formed by the closing blastopore will be called the 

 blastogroove. The two grooves lying in front of the blasto- 

 groove which have frequently been called the primitive groove 

 will be called the anterior and posterior germinal depressions. 

 Since these terms are perfectly colorless as regards homology 

 they leave the way clear for an unprejudiced discussion of the 

 meaning of the structures. 



The term, neural groove, which has often been applied to one 

 or all of these grooves just mentioned is not used in this con- 

 nection, because the neural nature of these three early grooves has 

 not been demonstrated. The true neural groove is a later struc- 

 ture appearing after the other grooves have begun to degenerate 

 and persisting as the faint narrow groove lying in the bottom of 

 the neural canal. 



The term, neural plate, will be used in its usual sense. The 

 division of this plate into well defined regions demands further 

 definition. The terms, hirn-platte and cephalic plate, which 

 have been loosely applied to the widened anterior end of the 

 plate, will be discarded for the term procephalic lobes, denoting 

 that part of the neural plate which lies in front of a distinct 

 transverse furrow which will be called the transverse cephalic 

 groove. The region behind this groove may be theoretically 



