DETELOPMENT OP PERIPATUS NOV^-ZBALANDI^. 267 



cavity is marked c in the figure. It ends blindly in front and 

 behind, and probably is homologous with the area -which Mr. 

 Sedgwick (1) calls the polar area in P. capensis, which, both 

 in position and structure, it closely resembles, with the excep- 

 tion of the fact of its being filled with yolk-spheres in the 

 New Zealand species. Fig. 7 passes through the posterior 

 end of the primitive streak, where it is thinning out, and the 

 groove is much shallower. These three sections bear a very 

 close resemblance to figs. 25 and 26 on PI. V of Mr. Sedgwick's 

 Monograph on the Cape species (1). The peripheral nuclei in the 

 region of the blastopore and primitive streak have a more or 

 less columnar form instead of lying flat against the side as 

 they do over the rest of the ovum. The anterior part of the 

 egg is enveloped in a single layer of flat nuclei. 



In an ovum of a slightly later stage the blastopore has 

 increased a little in length, the primitive streak is much 

 larger and more marked, the nuclei being very closely packed, 

 and the primitive groove is considerably deeper; the so-called 

 polar area has disappeared. This stage is the latest which 

 was present among the January eggs, except some quite old 

 embryos which were almost ready for birth. 



I have examined several series of sections of older embryos, 

 i. e. in which they were developed, but have not thought it 

 necessary to give an account of them, as the process of 

 development seems to be similar to that of P. capensis de- 

 scribed by Mr. Sedgwick (] ). 



The only point of interest in which it differs from that species 

 is that the first somite (i. e. that of the prseoral or antennal 

 segment) opens by a duct to the exterior in precisely the same 

 way and position as do those of the third to fifteenth segments, 

 80 proving it to be the nephridium of the segment with the 

 same relations as those of the posterior ones. This is shown 

 in figs. 10 and 11 ; in the former the opening of the duct to the 

 exterior just outside the nerve-cord is shown, and in the latter, 

 which is separated from the former by three sections, its opening 

 into the somite. The probability of the nephridial nature of 

 this somite was pointed out by Mr. Sedgwick. 



