ANATOMY AND DEVELOPMENT OF PERIPATUS CAPENSIS. 255 



that they simply indicate the length of the straight line con- 

 necting the respective points. 



This is the last embryo of our series of young stages. The 

 next oldest embryo was 3*2 mm. in length. It had ringed 

 antennse, seventeen (?j pairs of legs, and was completely dou- 

 bled upon itself, as in Moseley's figure. 



The pits into the cerebral ganglia and a mouth and anus 

 were present. There can be no doubt that the mouth and 

 anus of this embryo become the mouth and anus of the 

 adult. 



The important question as to the connection between the 

 adult mouth and anus, and the embryonic mouth and anus of 

 the Stage E, must, considering the great gap between Stage E 

 and the next oldest embryo, be left open. Meanwhile, we may 

 point out that the embryonic mouth of Stage E has exactly 

 the same position as that of the adult; but that the anus is 

 considerably in front of the hind end of the body in Stage E, 

 while it is terminal in the adult. 



If the embryonic mouth and anus do become the adult 

 mouth and anus, there would appear to be an entire 

 absence of stomodseum and proctodaeum in Peripatus, unless 

 the buccal cavity represents the stomodseum. The latter 

 is formed, as has been shown by Moseley, by a series of 

 outgrowths round the simple mouth-opening of the embryo, 

 which enclosing the jaws give rise to the tumid lips of the 

 adult. 



For our determination of the posterior and anterior ends of 

 each of these embryos, Stage A to E, we depend upon the 

 opaque tissue seen in each case at one end of the blastopore. 



In Stage A it has the form of a band, extending backwards 

 from the blastopore. 



In Stages B — D, it has the form of an opaque mass of tissue 

 occupying the whole hind end of the embryo, and extending a 

 short distance on either side of the posterior end of the blas- 

 topore. 



This opacity is due in each case to a proliferation of cells 

 of the hypoblast, and, perhaps, from the epiblast (?). 



