238 COMPARATIVE ZOOLOGY. 



the family Bovidoe, genus Bos, species Taurus ; the Deer 

 is of the family Cervidx, genus Cervus, species Virgini- 

 anus, if the common Deer is meant. 



The diagram on the opposite page roughly represents 

 (for the relations of animals cannot be expressed' on a 

 plane surface) the relative positions of the subkingdoms 

 and classes according to affinity and rank.* 



SERIES L— PROTOZOA. 

 Animals without cellular tissues (the body consisting of 

 a single cell), and with no true eggs. The body which 

 corresponds to the egg does not develop a blastoderm. 



Subkingdom I. — Protozoa. 



This division was proposed by Von Siebold in 1845, to 

 contain that vast cloud of microscopic beings on the verge 

 of the Animal Kingdom which could not be received into 

 the other subkingdoms. Though the division was at first 

 artificial and provisional, the name now has a very definite 

 signification. The classes composing it are not founded 

 on a common type, but are distinguished by the absence 

 rather than the presence of positive characters. Many 

 stand parallel to the Protophyta of the Yegetable World, 

 and no definite line can be drawn between them. 



Protozoans agree in being minute, aquatic, and exceed- 

 ingly simple in structure, their bodies consisting mainly 

 or wholly of the contractile, gelatinous matter called pro- 

 toplasm, or sarcode — the first homogeneous substance 

 which has the power of controlling chemical and physical 

 forces. They have no cellular organs or tissues, yet they 

 take and assimilate food, grow, and multiply, which are 



* The student should master the distinctions between the great groups, or 

 classes, before proceeding to a minuter classification. " The essential mat- 

 ter, in the first place," says Huxley, " is to be quite clear about the different 

 classes, and to have a distinct knowledge of all the sharply definable modifi- 

 cations of animal structure which are discernible in the Animal Kingdom." 



