164 THE MICROSCOPIST. 



markably tenacious of life, having in some instances re- 

 vived after having been kept dry for several years. 



M. Dujardin divides the Rotifera into four groups or 

 natural families : 



1. Those attached by the foot, which is prolonged into 

 a pedicle. It includes two families, the Floscularians and 

 the MdicertianS) in the first of which the sheath or cara- 

 pace is transparent, and in the other composed of little 

 rounded pellets (Plate XIII, Fig. 120). 



2. The common Rotifer and its allies, which swim freely 

 or attach themselves by the foot at will (Plate XIII, Fig. 

 121). 



3. Those which are seldom or never attached, the Bra- 

 chionians and the Furcularians. The former are short, 

 broad, and flat, and inclosed in a sort of cuirass ; the latter 

 are named from a bifurcated, forcep-like foot (Plate XIV, 

 Fig. 122). 



4. The Tardigrada or water bears. These have no 

 ciliated lobes, but are in other respects like their allies, 

 and seem to be a connecting link between the Rotifers 

 and worms. The segments of the body, except the head, 

 bear two fleshy protuberances furnished with four curved 

 hooks.* 



Y. POLYPS. The animals of this class were formerly 

 called Zoophytes, or animal flowers. They are the most 

 important of coral-making animals, although the Hydroids 

 and Bryozoa, together with some Algae, as the Nullipores, 

 share with them the formation of coral, which is a secre- 

 tion of calcareous matter. Dana's work on corals gives a 

 classification, of which we present a summary. 



A good idea of a polyp may be had from comparison 

 with the garden aster, the most common form of a polyp 

 flower being a disk fringed with petal-like organs called 

 tentacles. 



The internal structure, like the external, is radiate, and 



* Carpenter on the Microscope. 



