CHAPTER X 



STRUCTURE AND CLASSIFICATION OF ZOOPHYTES 

 (CcELENTERATA), SPONGES (Porifera), AND ANIMALCULES 

 (Protozoa) 



ZOOPHYTES (Ccelenterata) 



The old expression " zoophyte " was applied to branching 

 colonies of organisms regarding the animal nature of which doubt 

 existed, and which were looked upon as being intermediate be- 

 tween animals and plants. Here were included the forms already 

 briefly dealt with under the heading of Polyzoa (p. 436), but these 

 are of much higher structure than the 

 bulk of zoophytes, which may con- 

 veniently be grouped together under 

 the phylum now to be considered. 

 This embraces the Corals, Jelly- Fish, 

 Sea- Anemones, and other creatures 

 less familiar to the ordinary observer. 

 As a simple and easily obtained type, 

 it is customary to take the Fresh-water 

 Polype {Hydra) (fig. 286), which is 

 often found attached to pond-weeds, 

 or sticking to the glass of a fresh- 

 water aquarium. By leaving such an 

 aquarium in a brightly-lit window for 

 some time, one may often secure a 

 supply of these animals, which collect 

 on the side next the light. As they 

 are not more than about \ of an inch long, the naked eye alone 

 is not sufficient for their proper examination. Much can be made 

 out with a simple lens, but a compound microscope is necessary 

 to determine details. This is one of the numerous cases where 

 important results are to be obtained by means of cutting thin 

 slices with a razor, an operation which requires that the animal 



Fig. 286. — Green Hydra [Hydra viridis), 

 enlarged 



Vol. I. 



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