DEVELOPMENT OF THE NERVOUS SYSTEM 



527 



this form to be entirely ectodermal, the only question being at the 

 very early stages where it was impossible to distinguish absolutely 

 between the ectoderm and entoderm. Figure 40, of a 38 mm. speci- 

 men, gives practically the adult conditions. 



Fig. 9 A transsection through the hypophysis of a larva of Stage VIII. X 125. 

 Fig. 10 A transsection through the hypophysis of a larva of Stage IX. X 125. 



REFERENCES 



hyp., hypophysis 



inf., infundibulum 



pr. en., pre-oral entoderm 



s., space formed by the cephalic growth 

 of embryo 



SEGMENTATION 



A study of segmentation may well be divided into two parts, 

 namely, that bearing on (1) the medullary plate, and (2) the neural 

 tube. Neuromeres in each of the above stages have been described, 

 but the problem of tracing the one into the other has not been 

 satisfactorily completed. In the closed neural tube, investigators 

 have reached fairly definite and uniform results concerning the 

 definition, number, and relations of the neuromeres of the hind- 

 brain. There are less uniform conclusions on the fore-brain. 



