THE GROUPS OF ANIMALS 



261 



SUBPHYLUM II. CiLlOPHORA. Protozoa having cilia in some stage. 



Class I. Ciliata. Ciliophora with cilia throughout life. Paramecium. (Figs. 

 ]5. 132, 138, 214.) 



Order 1. Holotricha 

 Order 2. Heterotricha 

 Order 3. OHgotricha 



Order 4. Hypotricha 

 Order 5. Peritricha 



Class II. Suctoria. Ciliophora with cilia in young stages, tentacles in adult. 

 (Fig. 215.) 



Phylum 2. Porifera. — The sponges are roughly radial in form and 

 always diploblastic (two-layered), though many wandering cells are 

 found in a jellylike substance between the layers. The body wall is 

 always penetrated by many pores, which give the phylum its name. 

 These pores lead to chambers within, which may be single cavities extend- 

 ing from outside to inside, or may branch or connect with other cavities 

 in a complex system. The final opening through which the water leaves 



Fig. 216. — Elements of sponge skele- 

 tons. 1, spongin; 2-7, spicules. 



Fig. 217.1 

 A sponge. 



the body is called the osculum, and there may be many of these oscula. 

 Some of the chambers are lined by collared cells (Fig. 33, page 52). The 

 collared cells also possess flagella, by means of which a current of water is 

 kept up continuously in the same direction. Food organisms and oxygen 

 are brought, and wastes are carried away, by these currents. The 

 collared cells seize the food, digest it, and pass along much of the nutrition 

 to the other parts of the organism. 



The sponges all possess a skeleton, which in some consists of a host of 

 limy or siliceous spicules, in others of a network of horny (spongin) 

 threads (Fig. 216). It is this latter horny skeleton which makes the 

 ordinary bath sponge. 



Members of this phylum are all sessile; that is, they are attached to 

 other objects and do not move about. About a hundred and fifty species 

 live in fresh water, where they sprawl in irregular form over twigs or 

 logs. It is these fresh-water forms that reproduce by gemmules (page 

 170). The bulk of the phylum is marine, and they are found all over the 

 world. 



Courtesy of General Biological Supply House. 



