SIMILITUDE TO CORALS. 367 



wound, and the EscJiara Jl,aJ>ellaris^ a very curious pol yzoon of tlie same genus. The latter 

 is remarkable for the hood or helmet-like ovicells. About eleven species of this genus 

 are known. 



In the illustration on the opposite page is shown one of the most curious of the polyzoa, 

 named, from the external resemblance which its apertures present to the meshes of a net, the 

 Retepora, or Net-pored animal. The polyzoary of this species is hard, chalky, is only pierced 

 on one surface, and has so much the appearance of the true stony corals, that it might easily 

 be mistaken for one of these objects. It is a European species, and the specimen represented 

 of the natural size. 



The next interesting family of polyzoa is called Selenariadso, because they are round as 

 the full moon, or NorvaF s famous shield. In the circular form of the margin they all agree, 

 but differ considerably in their curvatures, some being with one side plane and the other con- 

 vex, while others are convex-concave, like a watch-glass, or, to speak more accurately, like the 

 lens technically called a meniscus. They are all remarkable for their very large vibracula. 



One of these creatures is called Gupularia lowei on account of its resemblance to a dome. 



A good example of a very shield-like genus of this family is the Selenaria maculata. The 

 reader will not fail to remark its exact resemblance to the target-shield used by many nations, 

 ancient and modern. It may be here mentioned that in this last-mentioned family the vibracula 

 are thought by some naturalists to act as locomotive organs. 



Our space is so rapidly drawing to a close, that it will be hardly possible to give much 

 more than a brief account of a few more interesting examples. 



IN the group of polyzoa I am going to describe, there is a great external similarity between 

 their forms and those of the true stony corals so familiar to us. It will, moreover, be found, 

 that in many details of their structure, there is a decided analogy between them and the true 

 zoophytes which will be described in the latter part of the work. 



In the Crisia eburna the arrangement of the cells is simple and elegant, and the various 

 branches are connected with each other by means of certain horny joints. The use of these 

 joints is, in all probability, to enable the polyzoary to resist the action of the waves, and so to 

 avoid the fractures which would probably result if the joints were as stiff and inflexible as the 

 cells. A similar provision will be seen in the Gorgonia, a zoophyte which will be described 

 on a future page. 



A remarkably constructed species, the Tdmonea atlantica, looks something like a. many- 

 legged spider, with its branches protruding from a rounded centre which represents the body 

 of that animal. 



A polyzoon remarkable for the profusion and great comparative length of the cells, is 

 termed Pustulopora deUcatula, the generic name being on account of the minute dots with 

 which the surface of the cells and polyzoary is studded, and the specific title in reference to 

 the delicate structure and soft brown hue with which it is colored. 



A stoutly-built polyzoon named ffornera, is notable for its resemblance to several corals. 



IN the accompanying illustration, the resemblance to the corals, the madrepores, and even 

 the stony habitations of certain marine worms, is very close and striking. 



Fig. A represents a polyzoon fancifully entitled Alecto, in honor of one of the Furies of 

 that name. It is seen of its natural size as it appears while spreading itself over the inner 

 surface of a shell. At Fig. B, a portion of the same species is shown as it appears when 

 magnified, and is given to exhibit not only the method in which the cells are sunk into the 

 polyzoary, but the mode in which the branches are developed from each other. 



At Fig. C is delineated a portion of the appropriately named Titbulipora serpens, a being 

 which has the cells even more elongated than in the Pustulopora, which has been lately 

 described. The singular resemblance between the lengthened cells of this species and the 

 hard shelly tubes of the well-known Serpula, so familiar on account of its scarlet and white 

 pi umes and marvellously engraved stopper, must be evident to every one who has seen the 

 little creature, or even noticed its empty habitation. 



