56 ACALEPIIS IN GENERAL. Part I. 



Ilvilroitls proper have no railiating tulies, while their Meduste buds have them 

 fully (levelo])e(l. I suppose the case to l)e this : That a 2)erfect Medusa has two 

 distinct structural elements, the disk or l)ell with its radiating tubes, and the pro- 

 boscis with the mouth, and that in II_ydroid conununities the different individuals 

 present one or the other of these two elements, singly developed or more or less 

 condjineil ; while their Medusa^ Inids have always the characteristic features of per- 

 fect Medusa^, and are always sexual, Avhereas the Ilydroids are never so, whether 

 the pi'oboscidal or the IjcU element be the more prominent. If this be true, then 

 the characteristic feature of a Diphyes connnunity consists in the more Medusoid 

 character of some of its Ilydroids, while the more numerous individuals resemljle 

 the common Ilydroids moi'c, and, like those, produce the sexual Medusae buds. We 

 have already seen, in the family of Tubnlaria^ (p. 4-")), analogous combinations of 

 characters ; some of the fertile buds of these Ilydroids Ijeing more Medusoid in 

 their structure than others. 



The peculiai-ities of the genus AJjyla (Calpe) seem to C(mfirm this view. We 

 have here also, as in most Diphyes, two so-called swinuning-1 jells, only that the 

 first is much smaller and less Medusa-like than the second, and that the so-called 

 Polyps of the ])endent string are not protected by sim}»le scales, 1jut l)y a cap 

 resembling the first swimming-bell, with this additional peculiarity, that the tentacles 

 arc more or less removed from the base of the Polyps. 



The genus Praya is very closely allied to the genus Diphyes, but its two swim- 

 ming-bells are placed side by side, and the pendent string consists of Ilydroids 

 with a, distinct helm-shaped bell, from which arise the Medus;vi buds. This string 

 of twin individuals, one of which is a Ilydroid with a helm-shaped bell and 

 another a genuine Medusa, has l)een described as a string of single individuals, 

 the Medusa buds being considered as their sexual organ, but with as little pro- 

 priety as in the genuine I)iphyi(la\ for these buds again ai-e themselves sexual. 

 The so-called single individuals of all Diphyide are not single lieings, but twins, 

 one of which is Ilj'droid, and the other Medusoid, in its structure; and these twins 

 drop together and swim about freely as independent individuals. 



In the genus Vogtia, the so-called swinnning-bells have a quadrangular shape, 

 somewhat like a, contracted Stanrojihora, and though no radiating tubes have been 

 described in tlu'in, I doubt not that they will be found when sought for. Below 

 the pyramid of these Medusoid Ilydiw, there are a few simple, sucker-like Ihdroids, 

 and from the lower part of the axis arise the sexual Medusa l)uds, with enormous 

 proboscides, covered either with eggs or spermatic cells, projecting far out of the 

 Medusa bell, as is sometimes the case with those Sarsias that are not detached 

 from their stem. (PI. XVII. Fii/s. l."!, 14. 1 •">. and 1(1) In the genera Ilippopodius 

 and Elephantopus, which are certaiidy distinct, though frequently considered as 



