286 



in contact with the bases of the epithelial cells, but for the most 

 part in the mesenchyme. It is the only collagenous tissue present at 

 this stage. The ectoderm consists of two rows of cells as on other 



Fig. 4. Longitudinal section through base of right balancer of a 7,5 mm embryo. 

 The plane of the section is transverse to the long axis of the embryo (of. Fig. 2). 

 b. c blood capillary, b. m basement membrane, ec ectoderm. X 440. 



parts of the body. Only 

 a few cell boundaries 

 were to be seen in this 

 preparation. 



Fig. 4 shows a section 

 through the base of the 

 balancer of a 7,5 mm em- 

 bryo, the plane of the 

 section being transverse 

 to the long axis of the 



Fig. 5. Transvei'se section 

 through balancer of a 7,8 mm 

 embrj^o. The section is near 

 the proximal end. b. c blood 

 capillary, bd blood corpuscle, 

 contains a large yolk spherule. 

 b.m basement membrane, ec. ecto- 

 derm. 7nes mesoderm. X^IO- 



body (cf. Fig. 2). It shows a two-layered ectoderm lined on the 

 inner surface by a thick basement membrane {h.m). Mesenchymal 



mes 



