514 p. E. SMITH 



a growth center. No neurenteric canal could be distinguished 

 nor would we expect to find one under these conditions. In the 

 head region the dorso-ventral diameter of the neural cavity up 

 to Stage VII is very narrow, the dorsal and ventral walls nearly 

 touching each other. By Stage VIII a well marked cavity is 

 present. 



Although in the closure of the medullary folds, Desmognathus is 

 apparently similar to some of the lower forms, this is not due, 

 I believe, to any phylogenetic relation but rather to the mechan- 

 ical influence of the large and compact mass of yolk and the small 

 space in which the processes of growth must take place. It is an 

 interesting example of the effect of mechanics which might lead to 

 a wrong phylogenetic interpretation. 



THE PINEAL REGION 



This term is used in the sense introduced by Minot ('01). It 

 includes the paraphysis, the posterior commissure and the struc- 

 tures in the roof of the fore-brain lying between them. This 

 region has received attention from numerous investigators so that 

 the literature about this rather peculiar portion of the brain is 

 quite extensive. That these investigators concur for the most part 

 in their results, although working on widely diversified forms, 

 attests the relative phylogenetic simplicity of this region. This 

 has enabled the structures to be homologized throughout the 

 vertebrate series. 



To contribute one more form to the series described, I have 

 traced the development of this region in Desmognathus. Several 

 stages have been modelled to show the topographical relations 

 and the intervening stages have been studied from cross and 

 sagittal sections. 



Description 



The foldings in the fore-brain and their relation to the neuro- 

 meres have been taken up under a discussion of ''Segmentation." 



At Stage IX (figs. 1, 37) a point in the development has been 

 reached when the parts of this region are unmistakable. Figure 1 

 is a medial section through the pineal region. For relations 



