van Beneden on Rabbit 



37 



been formed, and also that the canal of Lieberkiihn is the 

 invagination cavity and is therefore archenteron. In his view 

 the blastocyst of a six-day Rabbit before the primitive streak 

 begins to form is not a gastrula, but a blastula, Fig. 19. The 



Fig. 19. Diagrams to illustrate van Beneden's interpretation. 



A, Mammal; B, Elasmobranch. bl blastodisc; m merocytes; the lined area la 



the lecithophore. 



inner layer of cells together with the fluid van Beneden calls 

 lecithophore, and he says they are homologous to the unsegmented 

 yolk of an Elasmobranch with its merocytes. 



Fig. 20 after van Beneden. Rabbit eight days. Plate XIV, Section 14. 



Transverse section through embryonal area, end (endoderm) archenteric 



plate of van Beneden; lee lecithophore. 



Clearly if Riickert is right in ascribing the origin of the 

 merocytes to the accessory spermatozoa, this homology will not 

 hold good, but it might apply to the Teleostean egg. 



Gastrulation according to van Beneden occurs by invagination, 

 producing the groove along the primitive streak and the canal of 



