THE UNICELLULAR ORGANISMS. 73 



PLATE XVIII. 



THE UNICELLULAR ORGANISMS. 



Vorticella. 



FIG. I. A group of Vorticellae, showing the animal in various positions. A. 3. 

 For a summary of the numerous species of this prolific genus see Kent (113). 



FIG. II. The same animal, in the extended and retracted states. Surface views. 

 FIG. III. Another individual, drawn in optical section during the process of extension. 



FIG. IV. Two views of the same. In the right hand one (erroneously lettered 

 Fig. III.) a series of food vacuoles are drawn, one of them in the act of being ingested. 



The arrows indicate the course taken by these, and the top left-hand one marks the 

 point at which egestiou most frequently takes place. 



The left-hand figure represents the nucleus, after treatment with acetic acid and 

 magenta. 



(Figs. I. to IV., all drawn under Zeiss. D. 4.) 



FIG. V. The initial phase in the process of multiplication by fission. 

 Two hours later, two equal-sized organisms resulted from this. 



FIG. VI. An example in which two individuals, unequal in size, resulted from the same 

 process. 



The smaller one was drawn in the act of liberating itself. 



FIG. VII. The same, after liberation. 



FIGS. VIII. and IX. Two successive phases observed in the process of conjugation. 



FIG. X. (Erroneously lettered IX.) An encysted Vorticella. 

 (Figs. V. to X. all drawn under D. 2. The cilia are represented only in VI. and VII.) 



Amoeba. 



Figs. XI. to XVIII. represent successive phases in the life-history of an Amoaboid 

 organism, kept under constant observation for three days. See Appendix I. 



XI. The locomotor phase. 



At * the ectoplasm is seen in the act of protrusion to form a pseudopodium, the 

 endoplasm passed into it later and quite suddenly. 



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