CONCRESCENCE IN EMBRYO OF CRYPTOBRANCHUS. 247 



is formed in situ, so far as overgrowth and convergence are con- 

 cerned; about 1 6 of the posterior end of the embryo is formed 

 by the convergence of material lying in the region of the lips 

 of the blastopore; the remaining middle portion of the embryo, 

 about 60 in extent, is formed in connection with overgrowth 

 by the dorsal lip of the blastopore, with the possibility of con- 

 fluence. It is the possibility of confluence in this region that 

 we desire to investigate; also some details concerning convergence 

 and the movements of the neural folds. 



The concept of concrescence, especially in the earlier stages 

 of its history, has often been assumed to involve the idea of a 

 certain amount of preformation in the parts that are brought 

 together; they must be differentiated as the anlage of definite 

 organs. In the present paper I shall neglect entirely this phase 

 of the problem ; the term concrescence is here employed without 

 any implications as to the amount of differentiation in the regions 

 concerned. 



II. METHODS AND TECHNIQUE. 



Xearly all the previous experimental work on the problem of 

 concrescence has been done by mechanical methods: an injury 

 of some sort has been inflicted on the living egg and the result 

 in later stages noted. The usual mode of procedure has been to 

 prick the egg with a fine needle, making a slight puncture suf- 

 ficient only to establish a landmark by means of which the move- 

 ment of materials may be followed. 



The present study is an attempt to apply the method of vital 

 staining to the solution of this problem. The advantage of this 

 method is that extensive markings may. be made without in the 

 least interfering with the normal course of development. From 

 Goodale ('n) was obtained the idea of using Nile blue sulphate 

 for this purpose. On account of marked differences in the struc- 

 ture of the gelatinous envelopes of the eggs of the two species, 

 the method of applying the stain to the egg of Cryptobranchus 

 necessarily differs from that employed by Goodale for the egg of 

 Spelerpes. 



Nile blue sulphate in aqueous solution of the proper strength 

 produces on the egg or embryo of Cryptobranchus a very distinct 



