448 



WALTER HEAPE. 



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 XXIX, fig. 24. 



tr.St se&c. 



Explanation of "VVoodcut, 

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

 Mouse (after Kupffer) ; D, of House mouse (after Seleuka) ; 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. CUV., blastodermic cavity; ep., cpiblast ; hi/., hypoblast; i. m., inner 

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

 trager. 



There is, however^ a diflTerence in the future development. 



