PRACTICAL ZOOLOGy 2Q 



the cilia, note that the latter are confined to the margin 

 of the bell-shaped body ; the miniature vortex into which 

 food particles are drawn by the action of the cilia. 



With the high power, study the position and shape 

 of the large crooked nucleus, the motions of the single 

 contractile vacuole, the structure of the stalk, and the 

 ingestion of food particles (Fig. 1 1, b\ Some specimens 

 will probably be found in the state . of fission. The 

 early stages may be identified by the broadening of the 

 body transversely, the absence of cilia, and by a vertical 

 groove indicating the direction of division. Later the 

 two parts become more or less completely separated, 

 one having a circle of cilia around its lower portion. A 

 few minutes after the cilia are formed the animalcule 

 breaks away from its companion, leaving the latter in 

 possession of the stalk, and swims away by means of its 

 temporary locomotor cilia to select a site for attaching 

 itself and developing its own stalk (Fig. 1 1, a). 



Conjugation may sometimes be observed, and may be 

 recognized by the fact that a large stalked individual 

 has attached to the lower portion of its body a much 

 smaller nonstalked individual, which gradually merges 

 into the body of the larger animal and disappears. The 

 nuclei of the two individuals fuse together and fertiliza- 

 tion is thus accomplished, but the changes which take 

 place within the two cells during the process of conjuga- 

 tion can be demonstrated only upon specimens especially 

 prepared for this purpose, the method of preparation 

 being too intricate for beginners. 



Metazoa 



Porifera 



Material. Simple marine sponges maybe obtained of 

 dealers in laboratory supplies. ,Fresh-water sponges, 

 Spongilla (green) and Myenia (brown) are to be looked 



