MORrHOLOGY OF CYCLOSTOMATA. 323 



the part where the duct has been described above as weakest. 

 It is also the fact that repeated cell-multiplication takes place 

 at the outer rim of each Anlage of the pronephros. One might 

 suppose that the product of the cell-division would contribute 

 only to the growth of the Anlage itself aud has nothing to do 

 with the cord ; but this is not the case : the Anlage does not 

 grow at the outer (lateral) end, as it might seem, but by cell- 

 division within its own structure. I have never observed any 

 case of cell-proliferation along the dorsal edge of the lateral 

 plate in an intersomitic portion, although the cords appear, in 

 later stages, to have some connection with, that edge, when they 

 are fully establisiied (see the right side of figs. 9 and 10) ; this 

 connection thus is not primary, but secondary. The epiblast has, 

 from the first, no share in the formation of the cord, always 

 showing a sharp contour against the mesoblast below. 



There is thus no difficuliy in acceptim/ the view that the 

 connecting cord is formed of the intersomitic cell- outgrowths which 

 are budded out of the anterior and posterior rims of each Anlage 

 of the pronephros and are subsequently fused together. The cord 

 isj therefore, originally brought about by the conßuencc of the free 

 extremities of the Anlagen. 



Further development of the Anlage of the pronephros may 

 be intelligible by refering to fig. 18 which represents a sec- 

 tion through a little older embryo of Stage ii. The epiblast {ep.) 

 consists of a single layer of cubical cells as before ; the neural cord 

 (n.) is still solid. On the left side of the figure, the hind border 

 of the fourth myotome {pit. IV) is cut, while on the right, the 

 mid-plane of the fifth myotome is met witli. A comparison with 

 the corresponding parts in the younger stages (figs, o and 8) will 



