174 ASTEROIDAL ZOOPHYTES. 



CHAPTER IX. 



ASTEROIDAL ZOOPHYTES. 



Numerous modifications of the form and habits of the hydra or poly- 

 pus have appeared from the description and discussion in the preceding 

 pages. The like has been explained of several ascidian zoophytes, toge- 

 ther with the Ascidia itself and the Botryllus. I have ventured to depart 

 from systematic arrangement, and with the view of rendering the sub- 

 ject more easily understood, a certain latitude of expression has been as- 

 sumed throughout, which will, nevertheless, betray no one into error. 



We have seen that zoophytes are either simple or compound ; and 

 that some of the latter are composed of organic or living parts, and of in- 

 organic, or parts wherein no symptom of vitality is demonstrated. 



Besides the Hydraoid and Ascidian Zoophytes, there is still a third 

 class, more recently distinguished as Asteroidal Zoophytes, wherein none 

 are known in this country to exist as single animals, but all are compound, 

 and one section consists exclusively of organic parts, as the Lobularia. 



Another section consists of the combination of organic and inorganic 

 parts, the latter being a shell or bone, and this comprehends the Virgu- 

 la/ria and the Pennatula. 



The asteroidal zoophytes are composed of two distinct portions, first 

 a hydra or polypus, whose nature seems different in several respects from 

 that of the others which have been described. It is considerably larger 

 than that belonging to either the hydraoid or ascidian zoophytes ; the ten- 

 tacula are uniformly eight, of triangular shape, pectinated or bordered by 

 a number of short processes, and containing a stomach, from which several 

 slender tendrils, supposed to be intestinal organs, visibly descend to the 

 lower part of the zoophyte. 



