CHAPTER XI. 



ZOOPHYTES. 



299. THE term Zoophyte, although sometimes used in a wider 

 signification, is properly restricted to the class of Polypifera, or 

 polype-bearing animals, whose composite skeletons or "poly- 

 paries" have more or less of a plant-like form ; even the Potyzoa 

 (or Bryozoa) being now excluded, on account of their truly 

 Molluscan structure (Chap. XIII), notwithstanding the zoophytic 

 character of their forms and of their habits of life. The true 

 Zoophytes may be divided into two primary groups, the Hydrozoa 

 and the Anthozoa ; the Hydra (or fresh-water polype) standing 

 as the type of the one, and the Sea-Anemone as the representa- 

 tive of the other. As the Hydrozoa are essentially microscopic 

 animals, they need to be described with some minuteness ; whilst 

 in regard to the Anthozoa, only those points can be dwelt on, 

 which are of special interest to the Microscopist. 



300. The Hydra is to be searched for in pools and ditches, 

 where it is most commonly to be found attached to the leaves or 

 stems of aquatic plants, floating pieces of stick, &c. Two species 

 are common in this country, the H. viridis or green polype, and 

 the H. vulgaris, which is usually orange-brown, but sometimes 

 yellowish or red (its color being liable to some variation accord- 

 ing to the nature of the food on which it has been subsisting) ; 

 a third less common species, the H. fusca, is distinguished from 

 both the preceding by the length of its tentacula, which in the 

 former are scarcely as long as the body, whilst in the latter they 

 are, when fully extended, many times longer (Fig. 220). The 

 body of the Hydra consists of a simple bag or sac, which may 

 be regarded as a stomach, and which is capable of varying its 

 shape and dimensions in a very remarkable degree ; sometimes 

 extending itself in a straight line, so as to form a long narrow 

 cylinder, at other times being seen (when empty) as a minute 

 contracted globe, whilst, if distended with food, it may present 

 the form of an inverted flask or bottle, or even of a button. At 

 the upper end of this sac is a central opening, the "mouth," 

 and this is surrounded by a circle of tentacula or " arms," usually 

 from six to ten in number, which are arranged with great regu- 

 larity around the orifice. The body is prolonged at its lower 



