108 Mr. J. D. Dana on Zoophytes. 



mach suspended within the visceral cavity, and attached to the 

 sides of the polyp by a radiating series of vertical fleshy lamella?, 

 which are wanting in the Hydroidea. The visceral cavity is a 

 simple tube in the latter, and is radiated with vertical lamellae in 

 the former; but these peculiarities are also connected with the 

 modes of reproduction. We omit other less obvious points of 

 difference. 



II. Ovarian System. — In this system, ranking in importance 

 with the digestive, the absence of special organs with spermatic 

 and ovarian functions distinguishes the Hydroidea, and the ex- 

 istence of such organs the Actinoidea. No character can be of 

 higher value, or more marked in its attending peculiarities. 



Among the Actinoidea, there is a great variation in the number 

 of genital lainellse, and in the relative position of the two kinds, 

 the spermatic and ovarian. In the Alcyonaria there are uni- 

 formly eight in all ; in the Actinaria, either six, twelve, or more*. 

 In many of the latter division, if not in all, the two kinds of la- 

 mellse (spermatic and ovarian) are distinct : in some of the former, 

 the same lamella is ovarian above and spermatic below, or two 

 are spermatic and the rest ovarian ; or perhaps other conditions 

 may exist. There is good reason for separating the Alcyonaria 

 from the Actinaria, but not for making each division equivalent 

 in rank to that of Hydroidea. 



III. Process of Budding and Growth. — 1. We find that the 

 fact of species budding or not budding, is not connected in Zoo- 

 phytes with any peculiarity of structure that can be detected, and 

 farther, the transitions are gradual and frequent. This character 

 therefore, as it indicates no difference of concentration in the ner- 

 vous system, is entitled to little consideration as a means of di- 

 stinction in the classification of these animals : — it is no more 

 important here than in botany, where a plant consisting of a 

 single individual bud may be placed alongside of one which 

 consists of several. It may sometimes however be used to distin- 

 guish genera : yet in the genus Fungia there are a few species 



* A passage of the Actinia into the Alcyonaria may perhaps be observed 

 in the Lucernarice, which have a four- or eight-lobed summit ; and other 

 Actinia approximate to this lobed character. These lobes bear a number 

 of tentacles, or correspond to a number ; and hence analogy suggests that 

 possibly in the Alcyonaria each tentacle properly corresponds to two ten- 

 tacles or more, or to a lobe in the Actinice alluded to. This view is borne 

 out by finding in the larger Alcyonaria the tentacles having a size wholly 

 incompatible with the structure of the Actinaria ; for the writer has shown 

 in another place that in the Actinaria there are limits to the relation be- 

 tween the number of tentacles, as well as the width of interval between the 

 genital lamella?, and the size of the animal. Whether the analogy holds or 

 not, the facts show striking differences between the Actinaria and Alcyo- 

 naria. See further, ' Report on Zoophytes,' pp. 34, 123. 



