ON BUDDING IN POLTZOA. 549 



blastic derivative which forms the outer layer of the tentacular 

 sheath, the outer epithelium of the tentacles, the mouth area, 

 and the lining of the oesophagus j and with a hypoblastic deri- 

 vative which occupies itself with the inner lining of the stomach 

 and intestine. We may safely assert that the outer layer of 

 the incipient polypide is mesoblastic as it develops into the 

 inner layer of the tentacular sheath, the inner epithelium of 

 the tentacles (somatopleure), and into the investing sheath of 

 the alimentary canal (splanchnopleure), as well as into the 

 muscles of the future polypide. Nitsche and Hatschek show 

 for the Phylactolaemata, and the latter for Pedicellina, that 

 the nervous system is derived from an epiblastic invagination. 

 There are no observations for the Gymnolsemata, as to the 

 ganglion, but it is in such close contact with the lophophore 

 that we may safely assume its origin from that body. This 

 would, of course, give it an epiblastic derivation. 



Prof. G. J. Allman was, I believe, the first to promulgate the 

 view that the zooeciura and the polypide are distinct individuals, 

 at all events this statement is very generally accepted ; but it 

 seems rather incredible that generations of individuals 

 solely composed ofa digestive canal and its appurte- 

 nances, such as muscles and nerve ganglion, seg- 

 mental organ, and possibly generative organs, should 

 live within the body cavity of one persistent indi- 

 vidual which lacks these organs and only possesses 

 a body wall, funiculus (?) and body cavity.^ 



' Tbe analogies which have been drawn between this supposed phenomenon, 

 and the undoubted cases of physiological and structural differentiation amongst 

 the Hydrozoa, will not really hold good; for in these the buds, though still 

 connected, are all external, and their specialisation can readily be accounted 

 for ; whereas, in the other case, each successive internal so-called bud develops 

 within the body-cavity of its parent in such a manner as to have precisely the 

 same relations as if it really was its alimentary tract, and not a bud. It is 

 not easy to conceive how this could come about, nor is it rendered any easier 

 if we yet farther follow the distinguished author of this view, and regard the 

 zooecium as the host not only of a nutritive poIy|)ide, but also of male and 

 female individuals ; for Prof. Ailman suggests that even the testis and the 

 ovary are, save sexually, aborted polypides ! 



VOL, XXUI. NEW SEK, O O 



