82 HISTOEY OF BRITISH ZOOPHYTES. 



but the joints are without hinges. The stem and branches 

 are of the same material. Along the sides or at the upper 

 extremities of the branches we find the cup-like cells of 

 the polypes. Intermingled with the cells there are other 

 vessels, called vesicles, formed of the same material as the 

 cells, but widely distinguished from them by their larger 

 size and by their different shape. Those vesicles contain 

 the ovules 'from which another generation of polypes is to 

 spring. 



The polypidoms, when dried, are generally of a yellowish- 

 horny colour. The substance of which they are formed 

 seems analogous to horn. In a young state it adheres in 

 some degree to the pulpy substance of the animal, but it 

 afterwards become detached in consequence of its shrivelling, 

 and also in consequence of the movements of the animal 

 that it contains. Some distinguished naturalists argue that 

 this horny sheath is vascular and organized, and conclude 

 from this that the polypidom has a growth of its own inde- 

 pendent of the animal that inhabits it. But other natu- 

 ralists, no less distinguished, maintain, and apparently with 

 greater truth, that there is but one life and one plan of de- 

 velopment in the whole mass, and that this depends, not on 

 the polypi, which often fall off, as in Tubularia, but on the 



