DEVELOPMENT OF PEBIPATUS NOV^-ZEALANDIJ!. 271 



previous paper (3). In it one of the most remarkable features 

 was the presence of the yolk outside the embryo^ between it 

 and the vitelline membrane. It might be more correct and in- 

 telligible to consider this as ectodermic yolk. In P. capensis 

 protoplasmic strands are present, passing from the ectoderm 

 to the egg-shell, especially in the region of the dorsal hump, and 

 these very probably indicate that ectodermal yolk was present 

 at one time in this position. In the last chapter (supra, p. 125) 

 of his Monograph of the Cape species, Mr. Sedgwick states 

 that the ectoderm is much vacuolated and contains globules 

 which he believes to be yolk up to a comparatively late stage of 

 development. Thus it seems probable that both species wei'e pos- 

 sessed of ectodermal yolk. In the gastrula stage in both species 

 there is no sign of any trace of yolk which probably therefore 

 arises later. In P. novse-zealandise this yolk isso thick that 

 it completely obscures the external characters^ which cannot be 

 made out in surface view till the stage at which the appendages 

 are forming when the ectodermal yolk is almost completely 

 absorbed. As to the mode and time of origin of this ecto- 

 dermal yolk in P. novae-zealandiae I am not able to make 

 any statement, as in the youngest egg in which it is present it 

 is already well formed, and constitutes a very thick layer j and 

 I do not know whether it is derived in some way from the 

 central yolk, or whether it arises as a fresh formation in the 

 ectoderm cells. However, the fact that in both species it is 

 absent in the gastrula stage and appears later seems to point 

 to its being an ancestral feature in the development. This, as 

 well as many other points of interest in the development of 

 this interesting species, will unfortunately have to remain un- 

 explained until someone shall be fortunate enough to obtain 

 embryos of the intermediate stages. 



