120 ACALETIIS IN GENERAL. Part I. 



Medusa .state, is so strictly homologous to that of all other naked-eyed Medusa^, 

 that, even if it were ascertained that it undergoes a direct metamorphosis from 

 the egg to the perfect Medusa, I would not hesitate to consider it as a member 

 of the order of Ilydroids, since it has simple radiating chymiferous tubes, a circular 

 tube, and marginal tentacles closely connected with it, and provided with mere 

 pigment specks upon their base. 



It Avill require a more extensive knowledge than we now possess of the 

 develo])ment of all Hj'droids, before the relative standing of their various types 

 can definitely be ascertained. As far as our information goes, the rank of Hydroids 

 among themselves does not seem to be determined primarily by the production of 

 free Medusa?, since Campanularias produce free Medusa^ ; while among Tuljularitv Ave 

 have those which bring forth free Medusa?, and others which do not. The distinct- 

 ness of the medusoid and hydroid elements, without reference to the liberation of 

 the Meduste, seems more significant ; for, xniquestionably, a Physalia with its extra- 

 ordinary polymorphism has an organization inferior to that of a Sarsia Ijorn from a 

 Coryne. In the first case we have a very complicated community, it is true, but 

 it consists chiefly of low, heterogeneous elements variously comliined, and the Medusa? 

 buds themselves are of the simplest kind, and without tentacles ; while in the 

 second case the hydroid and medusoid elements are quite distinct, and the Medusa? 

 arising from the simple Hydrarium are as perfect as any other naked-ej'ed Medusa\ 

 The same may be said of Lizzia, Ilippocrene, and Hybocodon, all of which have 

 a limited and definite number of radiating chymiferous tubes, a limited and definite 

 number of tentacles or bunches of tentacles, all characters which seem to assign 

 to them a marked superiority over Tiaropsis and Thaumantias Avith their numerous 

 marginal tentacles which arise from Campanularia', that is, from Hydroids exhiljiting 

 already signs of polymorphism, Avhile the Hydraria from Avhich Sarsia, Lizzia, etc., 

 arise, consist only of one kind of Hydra*. 



It Avordd thus appear that the distinctness of the hydroid and medusoid elements 

 in this order is inverse to the polymorphism of their communities. The Medusce 

 buds of most Siphonoi)hora? play a rather indifferent part in their economy ; and 

 yet their prominence coincides with the degi*ee of comj^lication of the hydroid and 

 medusoid elements of their communities. Velella, the community of which consists 

 only of two kinds of Hydra\ 2?roduces distinct free Medusa^; while the Dijjhyida? and 

 the Physophorida\ in Avhich the hydroid and medusoid elements are most comj^letely 

 mixed, are also those which are most remote from the true type of Discoj^hora", 

 and resemble most, in their mode of living, the free locomotive Polyp communities. 

 But even as compound connuunities consisting of heterogeneous elements, it is 

 remarkable that those in which the medusoid elements j^i'evail are also the most 

 active, while those in which the hydroid elements are predominant, are more 



