THE DEVELOPMENT OP THE MOLE. 



05 



cells. The cavity of the arch (the secondary cavity) is filled up 

 more or less with cells derived from the outer layer, and thus 

 a condition is arrived at remarkably like the stage of develop- 

 ment in the Mole represented in the woodcut, Fig. b, and on 

 Plate VII, fig. 24. 



hl.cav. 



■tr.Si sect. 



D 



— see,c 

 tH.cav. inn. 



secc 



TH.cav. 



Explanation of Woodcut. 

 Diagrammatic representation of : — a, ovum of Rabbit ; b, of Mole ; c, of Field 

 Mouse (after Kupffer) ; D, of House mouse (after Selenka) ; e, of Guinea- 

 pig. A, B, c, and D are at a similar stage of development, e is at a 

 much earlier stage, before the formation of a secondary cavity. 



bl. cav,, blastodermic cavity; ep., epiblast ; hi/., hypoblast; i. m., inner 

 mass ; o. I., outer layer ; sec. c, secondary cavity ; ir., rudimentary 

 trager. 



There is, however, a difference in the future development. 



