ANATOMY AND DEVELOPMENT OP PERIPATCTS CAPENSIS. 257 



bryonic 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 prseoral lobes, and to the mesoblast of the 

 head.^ 



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 show that he himself 

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

 covery. 



" Although the mesoblastic groove of insects is not a gastrula, 

 it is quite possible that it is the rudiment of a blastopore, 

 the gastrula corresponding to which has now vanished from 

 development." (' Comparative Embryology,' vol. i, p. 378.) 



" Tracheata. — Insecta. It (the mesoblast) grows inwards 

 from the lips of the germinal groove, which probably represents 

 the remains of a blastopore." (' Comparative Embryology,' 

 vol. ii, p. 291.) 



" It is, therefore, highly probable that the paired ingrowths 

 of the mesoblast from the lips of the blastopore may have 

 been, in the first instance, derived from a pair of archenteric 

 diverticula." (' Comparative Embryology,' vol. ii, p. 294.) 



The facts now recorded were discovered in June last, only a 

 short time before Balfour started for Switzerland; we know but 

 little of the new ideas which they called up in his mind. We 

 can only point to passages in his published works which seem to 

 indicate the direction which his speculations would have taken. 



After speculating as to the probability of a genetic connec- 

 tion between the circumoral nervous system of the Coelen- 

 terata,and the nervous system of Echinodermata,natyelminthes, 

 Chsetopoda, Mollusca, &c., he goes on to say : 



"A circumoral nerve-ring, if longitudinally extended, might 



' "We have seen nothing in any of our sections which we can identify as of 

 so-called mesenchymatous origin. 



