Chap. 11. 



THE DIFFERENT RADIATA. 



Firj. 31. 



there Ijeiiig, in foot, only two kinds of indivi.lnals : the sterile ones, among which 

 that occnpving the eeutre of the commnnit}' is larger than the others, like the 

 top animal of the Madrepores, and around it, clustered together, a large numl^er of 

 smaller ones ; and outside, the large fertile ^.y. 32. 



individuals {Fifj. 32) from which MedusiB buds 

 arise that become free, and are very simi- 

 lar to the common Oceania among the 

 naked-eyed Medusce. This, at least, is the 

 case in Velella {Figs. 31 and 32), as 1 

 shall show hereafter more fully. Meanwhile 

 the wood-cut below {Fig. 33) represents an Oceania-like Medusa 

 that freed itself, with many others, from the larger fertile 

 individuals of the connnon Velella, of the 

 Gulf of Mexico, represented in Fig. 31. The 

 individuals forming the communities known as Velella and Por- 

 pita have no more the structure of Polyps than those of the 

 Physalia. They are genuine Hydroids. 



If from these we pass to the Diphyida-, we notice a long 

 strino- of heterogeneous individuals suspended trom one or two 

 larger elongated, bell-shaped individuals, com- ^;^ ^^ 



monly called the swimming-bells, and gen- 

 erallv considered as organs destined to move the whole com- 



Velella jiutica, Bosc. 

 n So-called mouth —aa So-called 

 tentacles. 



Fig. 33. 



Single so-called tentacle of 

 Velella mutica, Bosc, 



Bearing Medusa^ buds tl d. — a 

 Base of attachment. — b Blunt 

 end of the tentacle. 



Free Medusa of 



Velella mutica, Bosc. 



Proboscis. — b Radiating chy- 



miferoas tube. — c Circular 



tube. 



munity {Figs. 



Fig. 85. 



34 and 3^ 



But I believe that this view is not 

 correct, l:)ut that, on the contrary, these 

 so-called swinnning-bells are themselves 

 distinct individuals of one kind connected 

 with smaller individuals of other kinds, 

 forming together a community composed 

 of very heterogeneous elements. The 

 invaluable investigations of Gegenbauer 

 upon the development of Diphyes seem 

 to me to leave no doubt upon this point ; 

 for he has observed the whole develop- 

 ment of the egg of one of these animals, showing that the 

 process of segmentation of the egg terminates in the formation 

 of one of these so-called swimming-bells. Now, the product of 

 the egg, whatever it may be, cannot be a mere organ. It is 

 imquestionaljly a young animal ; and that animal, as represented by Gegenbauer, is a 

 genuine naked-eyed Medusa. It has the fom- characteristic radiatmg tubes, a cn-cular 



Galeolaria filiformis, Leuck. 



Diphyes quadrivalvis, Gegenb- 



( Gipiedfrom Gegenbaiter.) 



a b Anterior and posterior swimming- 



IjeUg. — c String of twin individuals. 



— d Feelers with, lasso cells. — ^ 



Ceecal termination or base of the 



connecting tube or axis. 



Diphyes Sieboldii, Kull. 

 (Copied from KOUiker.) 



a b Anterior and posterior swim- 

 ming-bells. — € Base of the 

 axis of the community. —c 

 Main axis of the community, 

 with young buds. — rf rf Fully 

 dcTcIoped buds, with their 

 feelers. 



