24 ZOOPHYTES. 



The vesicle of ovules in the Sertularidfe may generally be traced 

 to a particular polyp, from which it is developed ; in other instances, 

 it so grows from the stem, that it seems rather to belong to the colony 

 than to any distinct animal in it. The connexion between the polyps 

 through the tubular cavity is such, that individuality cannot always 

 be distinguished. 



15. The puUulation of young from the sides of a parent is the 

 usual mode of reproduction with the Hydra, though at certain seasons 

 simple ovules are produced. A minute protuberance first begins to 

 rise on the surface ; it lengthens and becomes a rudimentary 

 branchlet, with a tubular axis connecting with the tubular cavity 

 of the parent; shortly one or more tentacles begin to appear at the 

 summit of the forming branchlet, and soon the number is completed, 

 and the young polyp is perfected. It remains for a while attached ; 

 but when matured, the young leaves the parent to swim at large and 

 give birth to other young. They breed rapidly, and frequently new 

 shoots commence before the animal is detached from the parent; and 

 occasionally sprout on sprout is thus added, till a small compound 

 group is formed. These animals also bud out tentacles without pre- 

 vious tubercles, which finally become complete animals. 



16. Very similar to the above, in general principle, is the formation 

 of persistent buds, by the successive production of which the branch- 

 ing zoophyte finally results. There is at first a protuberance in which 

 the chyloid fluids gain access, and either move by vibration, or have 

 a kind of circulation up along the sides and down the axis ; after a 

 while the calicle forms, and the polyp extends its arms, and begins its 

 contributions to the body-coralline. The first polyp with which the 

 zoophyte commences thus gives out a bud, and this another; and so 

 a succession is formed, and the little stem is gradually lengthened ; 

 branchlets grow out, and the plume or miniature tree (fig. 2) is finally 

 completed. The whole may be the work of a few weeks, or months, 

 though they usually continue budding and growing for some years. 

 Before the zoophyte has reached its limits in size, the number of 

 polyps sometimes becomes immensely large. In a single specimen of 

 Plumularia (P. angulosa), collected by the author in the East Indies, 

 there are about twelve thousand polyps to each plumose branch ; and, 

 as the whole zoophyte, three feet long, bears these plumes, on an ave- 

 rage, every half inch, on opposite sides, the whole number of polyps is 

 not short of eight millions ; all the offspring of a single germ, and 

 produced by successive buddings. 



