18 



FIBST LESSONS IN ZOOLOGY. 



L.-T 



A solid central mass constitutes the nucleus (iV). 4 

 smaller form is called Chilodon (Pig. 13). 



The trumpet - animalcule (Sfentor) is 

 large enough to be detected with the un- 

 aided eye. This Infusorian attaches itself 

 at one end by a stalk, and builds up a 

 slight tube, into which it contracts when 

 disturbed. The Stentor may be sometimes 

 observed multiplying by self-division. 



The process of self -division takes place in 



two hours. Fig. 14, f, represents the final 



stage when the two individuals swim away 



separately, each assuming the original adult 



:_.C form, a. 



"We have thus seen that in the one-celled 

 animals there is a considerable range of 

 form. Their organs are few and of the 

 simplest kind, and yet primitive as the 

 Protozoans are, they vary 

 greatly in form and in hab- 

 its, and certain kinds which 

 grow in compound assem- 

 blages partially bridge over 

 the gap separating the one- 

 celled from the many-celled 



-A 



Fio. JS.— Parameci- 

 um caudatum. A. 

 view from the dor- 

 sal side magniBed 

 160 diameters. P, 

 the taU; T, the 

 throat; A, the pos- 

 terior opening of 

 the digestive cavi- 

 ty; CV, the anter- 

 ior, and Cv, pos- 

 terior contractile 

 vesicles; N, a solid 

 central mass or nu- 

 cleus; V, the large 

 vibratUe cilia at 

 the edge of the 

 mouth: F, masses 

 of food. 



A B 



Pio. 13.— Chilodon, magnified 600 diameters. A, seen from 

 beneath; B, seen sideways. 



animals. The one-celled animals form a branch of the ani- 

 mal kingdom called Protozoa, from the Greek words protos, 

 first, and zoon, animal, meaning primitive or simplest ani- 

 mals. They differ from all other animals in being formed 

 of a single cell. Nature is greatest in her smallest things. 



