18 ARTHITU DENDY. 



of its leiigtli, wliicli probably indicates the position in which 

 they will subsequently appear. 



There appear to be no sense-organs, and I have not satisfied 

 myself as to the existence of a nerve-ring. In life there is a 

 pink spot on the outside of the base of each tentacle group, 

 and the manubrium also is more or less pink in colour. 



(b) Development. — The medusEe are developed as hollow 

 outgrowths or " buds " from the branching stolons already 

 described, and each stolon may bear as many as half a dozen 

 at the same time in various stages of development. As soon 

 as one medusoid approaches maturity another bud (fig. 20 a) 

 appears on the stolon close to its point of attachment, ready 

 to replace the first when it falls off. 



The youngest buds observed are represented in figs. 20 a 

 and 18 b; each is a single hollow outgrowth of the stolon, 

 composed of ectoderm and endoderm, but the thick mesogloea 

 of the stolon disappears almost if not quite completely in the 

 bud (fig. 20). The ectoderm and endoderm also change 

 their character, becoming much more compact and solid- 

 looking, and staining much more darkly. 



In the next stage (fig. 18 c) the endocodon is formed from 

 the ectoderm at the apex of the bud. There is, in the 

 section represented in the figure, some appearance of invagi- 

 nation, but if not at first solid the endocodon speedily 

 becomes so. 



The endocodon grows inwards, and at the same time the 

 endoderm invaginates as if pushed before it (figs. 18, 10), 

 forming a deep cup. The bottom of this cup is then pushed 

 outwards again through the endocodon to form the hollow, 

 finger-like manubrium, which makes its appearance very 

 early (fig. 20). 



Meanwhile the cells of the endocodon arrange themselves 

 in a single layer over the outer surface of the manubrium, 

 the inner surface of the future subumbrella, and the inner 

 surface of the future velum (fig. 20). These layers are at 

 first in close contact, but ultimately the subumbrellar cavity 

 makes its appearance between them. 



