533 



CHAPTER XI. 



ZOOPHYTES. 



409. 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 ' Polyparies ' 

 have more or less of a Plant-like form ; even the Polyzoa (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 An- 

 tkozoa; the Hydra (or Fresh-water Polype) standing as the type of 

 the one, and the Sea- Anemone as the representative of the other. 

 As most of the Hydrozoa are essentially Microscopic animals, they 

 need to be described with some minuteness ; whilst in regard to 

 the Anthozoa those points only can be dwelt-on which are of special 

 interest to the Microscopist. 



410. 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. xiridis or Green Polype, and 

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

 yellowish or red (its colour being liable to some variation according 

 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. 274). 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 

 Tentacles or ' Arms,' usually from six to ten in number, which are 



