TRACE EAT A. 



335 



Imt Dolirn (No. 408) has 

 with some probability 

 thrown doubts on Kowa- 

 levsky's interpretations. 

 According to l3ohrn the 

 part of the serous envelope 

 which covers the dorsal 

 surface becomes thickened, 

 and gives rise to a peculiar 

 dorsal plate which is shewn 

 in surface view in fig. 184 

 A, do, and in section in fig. 

 185 A, do. The ventral 

 parts of the amnion and 

 serous membrane have either 

 been ruptured or have dis- 

 appeared. While the dorsal 

 plate is being formed, the 

 mesoblast, and somewhat 

 later the lateral parts of 

 the epiblast of the ventral 

 plate gradually grow towards the dorsal side and enclose the dorsal plate, 



FIG. 184. THREE LARVAL STAGES OF HYDRO- 

 PHILUS FROM THE DORSAL SIDE, SHEWING THE GRADUAL 

 CLOSING IN OF THE DORSAL REGION WITH THE FOR- 

 MATION OF THE PECULIAR DORSAL ORGAN do. (After 



Kowalevsky.) 



do. dorsal organ; at. antennae. 



vn- 



FIG. 185. THREE TRANSVERSE SECTIONS THROUGH ADVANCED 

 EMBRYOS OF HYDROPHILUS. 



A. Section through the posterior part of the body of the same age as fig. 184 A. 



B. Section through the embryo of the same age as fig. 184 C. 



C. Section through a still older embryo. 



do. dorsal plate; vn. ventral nerve cord ; al. meseuteron; ht. heart. 

 The large spaces at the sides are parts of the body cavity. 



