912 ANATOMY AND DEVELOPMENT 



part of the body to which it belongs), does not acquire the 

 normal relations of a blastopore, but presents only those 

 rudimentary features (deep groove connected with origin of 

 mesoblast) which the whole blastopore of other tracheates 

 presents. 



We think it probable that the larval anus eventually shifts 

 to the hind end of the body, and gives rise to the adult anus. 

 We reserve the account of the internal structure of these em- 

 bryos (Stages A E) and of the later stages for a subsequent 

 memoir. 



We may briefly summarise the more important facts of the 

 early development of Peripatus capensis, detailed in the preceding 

 account. 



1. The greater part of the mesoblast is developed from the 

 walls of the archenteron. 



2. The embryonic mouth and anus are derived from the 

 respective ends of the original blastopore, the middle part of the 

 blastopore closing up. 



3. The embryonic mouth almost certainly becomes the 

 adult mouth, i.e. the aperture leading from the buccal cavity 

 into the pharynx, the two being in the same position. The 

 embryonic anus is in front of the position of the adult anus, but 

 in all probability shifts back, and persists as the adult anus. 



4. The anterior pair of mesoblastic somites gives rise to the 

 swellings of the praeoral lobes, and to the mesoblast of the 

 head 1 . 



There is no need for us to enlarge upon the importance of 

 these facts. Their close bearing upon some of the most im- 

 portant problems of morphology will be apparent to all, and 

 we may with advantage quote here some passages from Bal- 

 four's Comparative Embryology, which shew that he himself 

 long ago had anticipated and in a sense predicted their dis- 

 covery. 



"Although the mesoblastic groove of insects is not a gas- 

 trula, it is quite possible that it is the rudiment of a blasto- 

 pore, the gastrula corresponding to which has now vanished 



1 We have seen nothing in any of our sections which we can identify as of so- 

 called mesenchymatous origin. 



