20 



ADAM SEDGWICK. 



quently formed by the development of a lumen extending from 

 the body cavity into the intermediate cell mass. 



The features of the stage of development now reached are well 

 known ; it is that of the S-shaped cords of cells which have been 

 so often described. In the adjoining woodcut is represented part 

 of one of these S-shaped strings, showing clearly the above 





■50 



Transverse Section through the Trunk of a Buck Embryo with about 

 tvoenty-four Mesoblasiic Somites. 

 am. amnion ; so. somatopleure ; sp. splanchnopleure ; wd. Wolffian duct ; 

 5^. segmental tube ; ca.v. cardinal vein ; ms. muscle-plate ; sp.g. spinal 

 ganglion; 5/j.c. spinal cord ; cA. notochord ; «o. aorta; Ay. hypoblast. 



features of a tubule, &c., viz. — (1) the Wolffian duct, in which a 

 lumen has appeared ; (2) the outgrowth from it to the inter- 

 mediate cell mass forming the upper limb of the S ; (3) the 



