408 



I have also made some supplementary observations on Ambly- 

 stoma, Diemyctylus and Torpedo ocellata. I have found the meta- 

 meres readily enough in the very early stages of all these forms. 

 Although they are known to occur at a later period in all these 

 forms, so far as I know, their presence has not been recorded in 

 stages with abroadly expanded neural plate or a widely open neural 

 groove; but anyone who will study well preserved material 1 ) may 

 find these structures in the earliest stages. Of course, the metameres 

 are more easily seen if the embryos are placed over a black non- 

 reflecting surface and then well illuminated from above. 



Fig. 11, shows a camera sketch of an Amblystoma egg just after 

 the neural folds are formed, and while they are broadly expanded. 



Pig. 11. Egg of 

 Amblystoma punctatum 

 just after the formation 

 of the medullary folds. 

 The folds are shown to 

 be segmented as in 

 Squalus acanthias. 



The folds are divided, throughout their length, into a series of seg- 

 ments with no especial distinguishing features between those of the 

 head and those of the body region. It is interesting to note that 

 there are 10 or 11 of these segments included in the very broadly 

 expanded part of the embryo — that is counting from the point where 



1) I am indebted to Professor Reigbard, of the University of 

 Michigan, for Amblystoma, and to Dr. E. 0. Jordan, of the University 

 of Chicago, for the most embryos. Torpedo ocellata was obtained from the 

 Zoological Station at Naples. 



