38 BY THE DEEP SEA. 



almost innocent of organs. This form of structure is generally 

 referred to as a Polypite, and its appearance has been made 

 familiar by the descriptions and figures of the Hydra or Polyp 

 of our stagnant fresh-water ponds. From their general agree- 

 ment in structure with the Hydra, the creatures to which much 

 of this chapter will be devoted, are called Hydroid Zoophytes. 

 There are, however, but few species that occur solitarily, like 

 the Hydra. In most cases they are associated in inseparable 

 colonies. The egg of a zoophyte gives rise, it is true, to an 

 organism resembling Hydra, but this individual does not long 

 remain solitary ; it produces many buds, which rapidly develop, 

 and in turn produce other buds, so that before long there is a 

 colony that may number its thousands of polypites. How- 

 ever numerous the individuals may be, we may be sure that 

 the colony has been the production of a single egg. One came 

 from that egg, but all the others were produced vegetatively by 

 budding from the original polypite, or as later generations from 

 such bud-originated polyps. 



A slight examination of such a colony will show that the 

 polypites themselves are held in association by an investing 

 substance (can os ire], which takes the form of a living tube 

 of thin flesh, which adheres to rock or shell or seaweed, acting 

 as a support for the community, and also reproducing the 

 polypites. It consists of two distinct layers, an inner and an 

 outer, and sometimes there is a third layer of a different kind 

 between these two, muscular in character. In most cases the 

 outer wall of this tube secretes a sheath of a substance called 

 Mtin, of which the external skeletons of insects are composed. 

 This sheath is known as the polypary, because into it the indi- 

 vidual polypite withdraws itself. It is this polypary that the 

 sea-side visitor finds attached to weeds or shells, and concludes, 

 from its moss-like aspect, it is a seaweed, and probably adds it 

 to his collection as such. 



Now if we get down among the rocks near low-water, and 

 look among the coarse brown weeds, we shall not look long 



