ANATOMY AND DEVELOPMENT OF PERIPATTTS CAPENSIS. 253 



Stage D. — The next stage is Balfour's stage, and has been 

 already described. 



The length is 1-34. 



It will be observed, on comparing it with the preceding em- 

 bryos, that while the anterior pair of somites in figs. 35 and 

 36 lie at a considerable distance from what we have called the 

 anterior end of the embryo (a), in the embryo now under con- 

 sideration they are placed at the anterior end of the body, one 

 on each side of the middle line. We cannot speak positively as 

 to how they come there, whether by a pushing forward of the 

 anterior somites of the previous stage, or by the formation of 

 new somites anteriorly to those of the previous stage. 



In the next stage it is obvious that this anterior pair of so- 

 mites has been converted into the prseoral lobes. 



The anterior of the two openings to which the blastopore 

 gives rise is placed between the second pair of somites ; we 

 shall call it the embryonic mouth. The posterior opening 

 formed from the blastopore is elongated, being dilated in front 

 and continued back us a narrow slit (?) to very near the hind 

 end of the embryo, where it presents a second slight dilatation. 

 The anterior dilatation of the posterior open region of the 

 blastopore we shall call the embryonic anus. 



Lately, but too late to be figured with this memoir, we have 

 been fortunate enough to find an embryo of apparently precisely 

 the same stage as fig. 37. We are able, therefore, to give a 

 few more details about the stage. 



The measurements of this embryo were : 



Length of whole embryo ..... 



Distance from front end of body to front end of moutli 



„ embryonic mouth to bind end of embryonic auus 



„ from hind end of embryonic anus to bind cud 



of body ..... 



Length of embryonic anus ..... 



„ part of blastopore behind embryonic anus . 

 Greatest width of embryo ..... 



Stage E.— In the next stage (figs. 38 and 39) the flexure 

 of the hind end of the body has considerably increased. The 



