CLASSIFICATION OF THE PROTOZOA 2/ 



The form and structure of the nucleus vary exceedingly in different 

 species ; there are elongated, kidney-shaped, or even ramified nuclei as well 

 as spherical or oval ones ; in addition to vesicular - shaped nuclei with a 

 distinct nucleolus and incidentally also with a nuclear framework, we also 

 frequently come across homogeneous and more solid formations. The nuclei 

 are always differentiated from the protoplasm by their reactions, particularly 

 in regard to certain stains. 



The nucleus plays the same part in the life of the single celled organ- 

 isms as it does in the cells of the metazoa and metaphytes ; it appears 

 to influence in a certain manner all, or at least most of, the processes of life, 

 such as motility, regeneration, growth, and apparently also digestion ; its 

 principal influence, however, is exercised in the propagation of the cells, as 

 this is always brought about by the nucleus. 



The PROPAGATION of the protozoa is effected either by division or by 

 means of direct budding. In division, which is preceded by direct or 

 indirect (mitotic) division of the nucleus, the body separates into two, 

 several, or even a great many segments ; in this process the entire sub- 

 stance of the body is involved, or a small residual fragment may be 

 left which does not undergo further division and finally perishes. In the 

 budding method of multiplication a large number of buds are formed either 

 on the surface or in the interior of the creature. Where divisions or 

 buddings follow one another rapidly, without the segments separating imme- 

 diately after their production, numerous forms develop, which are unlike the 

 parental forms, and these are termed swarming spores or spores. Divisions 

 imperfectly accomplished lead to the formation of protozoal colonies. 



Sometimes encystment' takes place previous to division ; frequently, also, 

 sexual processes appear, such as the union of two similar (isogamia) or 

 dissimilar (anisogamia) individuals ; the union may be permanent (copula- 

 tion), the process being comparable to the fecundation of the ovum by 

 a spermatozoon, or the union may be transient (conjugation) ; after the 

 exchange of portions of the nucleus the couple separate, to multiply indepen- 

 dently of each other. Sometimes there is an ALTERNATION OF GENERATION, 

 through there being several methods of propagation combined in the same 

 species, either conjugation or copulation being practised ; the different 

 generations may thus differ considerably in certain cases. 



Protozoa inhabit salt water as well as fresh water ; they are also 

 found on land in very damp places, and invade animals as parasites. 



CLASSIFICATION OF THE PROTOZOA. 



Class I. Rhizopoda (Sarcodina). Protozoa, the body substance of which 

 forms pseudopodia ; most of them are capable of developing chitinous, chalky, 

 or gravelly coverings or frameworks, which, however, permit the protrusion 

 of the pseudopodia either over the entire periphery or at certain points. 

 They possess one nucleus or several. 



1 Independently of propagation, many protozoa protect themselves from death 

 by encystment when the water in which they are living dries up ; in this condition 

 the wind may carry them over wide tracts of land. 



