70 MANUAL OF ZOOLOGY. 



the Calclspongicz) the adult sponge never consists of more than 

 a single osculura and the pores belonging to it, constituting what 

 Hseckel terms a single "person." Most sponges, however, 

 form a " stock," consisting of several such " persons" united 

 together. 



CHAPTER VI. 

 INFUSORIA. 



The Infusoria of many writers comprise many of the lowest 

 forms of plants — such as the Diatoms — together with the Hoti- 

 fera, a class of minute animals now known to belong to the 

 Anntdoida. By modern writers, however, the term Infusoria 

 is used strictly to designate those Protozoa which possess a 

 mouth and rudimentary digestive cavity. They are, for this 

 reason, often called collectively the "stomatode" /V^te(7a, in 

 contradistinction to the remaining members of the sub-kingdom, 

 which are all "astomatous." The so-called "suctorial" lAfu- 

 soria (Acuietcs), however, appear to have no definite oral aper- 

 ture ; and the same is the case with the parasitic Opalina, 

 though there is great doubt as to the propriety of placing this in 

 the Infusoria at all. The name Infusoria itself is derived from 

 the fact that the members of the class are often developed in 

 organic infusions. 



The Infusoria, or Stomatode Protozoa, maybe defined as Pro- 

 tozoa which are mostly provided with a mouth and riidimentary 

 digestive cavity, which do not possess the power of emitting pseu- 

 dopodia, but which are furnished with vibratile cilia, or with 

 contractile filaments. They are mostly microscopic in size, and 

 their bodies usually consist of three distinct layers. 



The Infusoria may be divided into three orders — viz., 

 Suctoria, Ciliata, and Flagellata, of which the second comprises 

 the majority of the members of the class, and alone requires 

 much consideration. 



I. Order Ciliata. — This order comprises those Infusoria 

 in which the outer layer of the body is more or less abundantly 

 furnished with vibratile cilia, which serve either for locomotion 

 or for the procuring of food. Besides cilia, properly so called, 

 some of the ciliated Infusoria are provided with styles or jointed 

 bristles, which are movable, and subserve locomotion ; whilst 

 others have little hooks or uncini, with which they can attach 

 themselves to foreign bodies. As types of the order, Paramce- 



