ZOOPHYTES. 



15 



no radiated structure was externally apparent. In the present 

 class, it begins to be manifested, not in the form of the body, 

 but in the arrangement of the parts surrounding the mouth. 

 These organs, or tentacula, being capable of considerable 

 distension, and being used for the capture of food, probably 

 suggested to the Greek naturalists the application to the 

 animals of the word l ' polypi?"* the same which they applied 

 to the many-armed Cuttle-fishes, to which externally they 

 bear some resemblance. 



The Zoophytes or Polypes, for by both of these terms are 

 they still designated, may be arranged in four great divisions, 

 to each of which in turn our attention may be briefly directed. 



ORDER I. HYDROIDA.* 



IN the first family (Hydraidce) of the present order, is found 

 the common fresh-water Hydra (Fig. 7), a singular being, 

 whose history is more strange than the strangest fairy tale. 

 Two species are abundant in 

 pools and ditches during warm 

 weather; one (H. fusca), fur- 

 nished with tentacula capable 

 of being distended many times 

 the length of its body; the 

 other ( H. viridis), with a shorter 

 tentacula, and of a greenish 

 colour. Seen in its contracted 

 state, on the lower side of a 

 leaf or a twig, floating on the 

 water, it appears a little piece 

 of jelly, not larger than the 

 half of a pea. By extending 

 and contracting its body, it can 

 move along, and change its 

 place at pleasure, executing 

 a variety of movements not unlike those of the Caterpillars 

 hereafter mentioned as the * ' geometric. ' ' When it is engaged 

 in taking food, its favourite position seems to be the vertical, 

 which is maintained by a singular proceeding. The tail, or 



PART i. 



* The term means "Hydra- like." 

 B 



