520 BERTRAM G. SMITH 



observations on living material. Some comparisons with Nec- 

 turus have been given in a previous paper (Smith '11 a). Late 

 stages of Cryptobranchus japonicus have been figured by Ishikawa 

 ('04 and '08) and de Lange ('07). 



Stage 16: (figs. 235 to 237). This stage is reached about eight- 

 een hours later than the beginning of Stage 15. It is character- 

 ized by closed neural folds which are still more or less separated 

 by a median groove. Ganglionic ridges are forming at the sides 

 of the brain. The blastopore is no longer a transverse slit, but 

 a small round orifice which probably represents the definitive 

 cloacal opening. Up to this time the great majority of the eggs 

 have retained the 'vitelline membrane.' During Stage 16 or 

 slightly later this covering usually becomes ruptured as a conse- 

 quence of the growth of the embryo and is finally cast off. 



During the gastrula and open neural groove stages, careful 

 observations have been made to test the presence of cilia on the 

 ectoderm, with absolutely negative results. Currents of water 

 produced by ciliary motion may be detected through the move- 

 ments of yolk particles within the vitelline membrane when this 

 is present, or by means of powdered carmine added to the water 

 in cases where the vitelline membrane has been shed. At the 

 time when the neural folds are closing, cilia are present on the 

 sides of the body and the ventral surface of the yolk sac, but are 

 absent from the neural folds. The general direction of the ciliary 

 currents is toward the posterior end of the body. 



Stage 17: (figs. 238 to 2Ii.2). This staee is reached about a 

 day later than Stage 16. The neural folds are definitely closed 

 and the head well upraised. The optic vesicles are indicated 

 by slight paired expansions of the anterior part of the brain. 

 In some embryos the anlage of the pronephros is apparent through 

 an elevation of the overlying ectoderm. Cilia are absent from 

 the dorsal surface above the neural tube but are quite generally 

 present elsewhere and are particularly strong or numerous on 

 the dorsal surface of the body, lateral to the neural tube. In 

 general the beat of the cilia along the sides and ventral surface of 

 the body is backward. 



