Morphological Studies. 777 



nerve is wrong and misleading. How does an ordinary nerve grow ?^) 

 In horizontal sections the mode of growth of the lateral nerve is seen 

 to be as I formerly described it (36, pp. 19 — 20). Transverse sections 

 of embryos, and on such sections Prof. Dohrn seems to have chiefly 

 relied, are valueless for deciding this point. 



But I must now close. The researches in hand during the past 

 two or three years in addition to other results, here rendered more 

 and more certain the view that the nose and ear are specially modi- 

 fied parts of the system of lateral or branchial sense organs. And 

 there does not appear to be any evidence for any other view of their 

 homology. If there be evidence to show that the nose and ear are 

 modified gill-clefts, it ought to be produced. And regarding the gill 

 nature of the ear Profs. Dohrn and Froriep ought either to endeav- 

 our to establish or to abandon their position. 



Though I agree with many of Dohrn's doctrines and conclusions, 

 I cannot support the gill-cleft nature of nose, ear, or hypophysis. 



The true morphological nature of all three now appears to be 

 clear, and personally, if I persist in my views, it is not because they 

 are mine, but because they are so far the most satisfactory and most 

 probable. 



Finally, I must once more point out that van Wijhe's researches 

 on the development of the olfactory nerve, as described in the intro- 

 duction, have not the bearings on the question of the morphology of 

 the nose which van Wijhe's ascribed to them. They support the 

 view that the nose is the homologue of a segmental lateral sense organ, 

 and show that its nerve is homologous with the sensory portion of a 

 cranial segmental nerve. In possessing an epiblastic origin apart from 

 the central nervous system as described by van Wijhe (55) the ol- 

 factory nerve agrees with any other cranial segmental nerve. In brief, 

 the olfactory nerve (better ganglionic foundation) is derived from two 

 sources (lateral ganglion and neural ganglion) just as I recently stated 

 to be the case for all true cranial segmental ganglia (37). 



1) This question is answered very differently by different morpho- 

 logists : see the recent memoirs of Profs. Dohkn and His and of myself. 



