178 The Philippine Journal of Science i9i8 



moner species, but even there the principle does not fall, be- 

 cause he is able to recognize them at any stage of their life 

 cycle. Compared with the whole, especially in regard to the 

 Sarcodina and Mastigophora, the number of species in which 

 it is possible to do this unerringly is not so large as might be 

 imagined. Paramecium seen a few times is generally quickly 

 recognized even by the student, and the same may be said of 

 Vorticella, Spirostemum, or some of the other relatively mono- 

 morphic species. But there are many protozoa that may be 

 amoeboid at one stage in their life cycle and flagellated at another ; 

 or witness the numerous striking form changes in Plasmodium,, 

 Coccidium, Polystomella, or even as familiar a form as Arcella 

 during the course of their life cycles. These changes in form 

 are of such a pronounced nature in some species as to lead the 

 inexperienced worker to designate as a new species a cell that 

 may merely represent a stage in the life cycle of some already 

 well-known species. Such mistakes have been even committed 

 by experienced workers. No species of protozoa is absolutely 

 monomorphic. Some, it is true, have a very stable morphology, 

 but even there polymorphism may express itself in no more 

 pronounced way than in slight but none the less constant varia- 

 tions in size at definite periods of the life cycle. 



The placing of a protozoon in one of the great groups may 

 even involve the arbitrary naming of some stage in its cycle 

 as the^ "adult" stage. The determining of the protozoan adult 

 is not nearly so simple a matter as it is in the case of the meta- 

 zoon, where sexual maturity is a convenient landmark, and it 

 sometimes happens that a given species may be placed in either 

 one of two subphyla with perfect propriety. This is particularly 

 true of some of the simpler amoebae and flagellates. 



And the protoplasm through various stages of vitality. — In 

 other words, the physiological vigor and activity of the organism 

 is not constant throughout its entire life cycle. This introduces 

 the question of the immortality of the protozoan cell, which was 

 raised by Weismann in his contention that every protozoon was 

 a potential germ cell. This view has been vigorously combated 

 by Calkins, who has reviewed the situation in a paper - following 

 that of Woodruff and Erdmann ' on "endomixis" in Paramecium. 



- Calkins, G. N., Cycles and rhythms and the problem of "Immortality" 

 in Paramecium, Am. Naturalist (1915), 49, 65. 



^ Woodruff, L. L., and Erdmann, Rhoda, A normal periodic reorganization 

 process without cell fusion in Paramecium, Journ. Exp. Zool. (1914), 17, 

 425. Erdmann, Rhoda, and Woodruff, L. L., The periodic reorganization 

 process in Paramaecium caudatum, ibid. (1916), 20, 59. 



