CLASS HYDROZOA. II 



These organs are doubtless a rudimentary form of circu- 

 latory apparatus. 



There are no distinct organs of digestion, nor breathing 

 organs, nor nervous system, and no traces of a circulatory 

 system, beyond the little contractile chambers just men- 

 tioned. 



Paramoecmm has the power of multiplying itself by 

 dividing into two parts, either transversely or longitudin- 

 ally (fig. 2, B, C) ; but it can also produce young by 

 means of eggs. 



Eecapitulation of Essential Chaeactees. — The 

 body is usually composed of three distinct layers, and is 

 generally provided with the little vibrating filaments which 

 are known as "cilia." A mouth is present, but there ia 

 no distinct stomach or body-cavity. There are no diges- 

 tive or respiratory organs, and no nervous system, and the 

 only traces of a circulatory system are to be found in one 

 or more little pulsating sacs or chambers. These charac- 

 ters distinguish the class Infusoria as a whole. 



CHAPTER IV. 



class HYDROZOA. 



The animals which compose this class are for the most 

 part inhabitants of the sea; and, from their small size, 

 or their plant-like appearance, or again, their living far 

 from land in the open ocean, they can hardly be said 

 to be at all known in general. As the type of this class 

 we shall take a small and abundant form which occurs in 

 many ponds and lakes in Europe, namely, the common 

 Fresh -water Polype {Hydra mdgaris), from which the 

 name of the entire class is derived (Greek, hudra, a 

 water - dragon, hence a Fresh -water Polype; zoiin, an 

 animal). 



