Lat.Cd. 



I.O'rt. Cd. 5 2 Ko.0. Ep.Po. 



S.Orh.CJ. I.OruCJ. f^.n,. f^.O. 



I I , / I 



Medl IZ. R'.Supt. 5 4- 



//5C.X. 



Fig. 52 Surftice view of a 27 mm. embryo. Note that the dorsal cord has 

 broken into short segments and that the accessory organs are now fairly promi- 

 nent. Squalus. From a sketch by Otto Swezey. 



Fig. 53 Ventral view of the same specimen showing distribution of the sen- 

 sory cords on the under surface of the head. Note the rudiments of two short 

 lines of pit organs (Pi.O.) just anterior to the yolk stalk. Squalus. From a 

 sketch by Otto Swezey. 



Fig. 54 Porso-lateral dissection of the medulla of a stage similar to the one 

 shown in figure 53. Note that the lateral nerve is separated into two main divi-. 

 sions. The upper division supplies the accessory organs. X 22. 



53 



