1892.] MICROSCOPICAL JOURNAL. 243 



In surveying the Protozoa in this way one cannot escape noting 

 the parallel between the phylum, as a whole, and the single bodies 

 of the Metazoa. In any of the higher animals the single egg gives 

 rise to a vast number of cells, some of which specialize the meta- 

 bolic power, while others specialize motor and still other sensory 

 functions. So in the Protozoa, in its history as a phylum, the 

 descendants of the ancestral form have diverged in consequence 

 of specializations, but in the cells of a higher animal a union and 

 subordination and division of labor makes a body of many parts 

 possible, while in the Protozoa the cells constantly sunder and 

 scatter. 



It is a question whether the Protozoa are still undergoing evo- 

 lution, and in answer it must be said that no conclusive evidence 

 has been adduced. In the absence of proof it must be noted that 

 the older a group is the less liable its members would appear to 

 be to change, for the same reason that conservatism is always char- 

 acteristic of old age, viz., the law of habit. And yet while this 

 would argue against the probability of change most, if not all, 

 biologists are inclined to admit that changes in structure can take 

 place at any time and become the beginning of a new line of evo- 

 lution, whether thev be changes born in a body which all admit 

 are likely to be transmitted, or acquired variations which all biolo- 

 gists do not consider transmissible. The cultivation of bacteria 

 and the alteration of their powers is a field of investigation border- 

 ing on this ground, and the latest researches seem to indicate that 

 among bacteria at least there are few fixed specific boundaries. 



Explanation of Plate. 



Fig. 1. Amoeba proteus ; 2. A. radiosa ; 3. f>rmation; 16 Peridinium uberrimum ; 17. 



A. villosa; 4. A. polypodia in act of division ; Noctiluca miliaiis ; 18, 10, 20. Codosiga um- 



5. Difflugia pyriformis ; 6. Hyalosphenia bellata, colony, single cell and cell division ; 



cuneai ; 7. Actinosphcrium eichornii ; 8. Cla- 21. Paramecium aurelia; 22. Stentor; 23. 



thorulina elegans ; 9. Rotalia sp. ; 10. Spiro- Pyxicola affinis ; 24, 25, 26. Vorticella sp. 



iina sp. ; 11. Gromia oviformis ; 12. Lieber- expanded and retracted, and series showing 



kuhnia; 13. Gregarina gigantea ; 14. Gre- absorption of conjugate, 

 garina flattarum ; 15. Monocystis agilis, spore 



A Bacteriological Potato-Section (hitter. 



By CHARLES F. DAWSON, M. D., 



WASHINGTON, I). C. 



.Several methods of preparing potatoes for a culture medium 

 are now in vogue, each having more or less efficiency, and a 

 variable amount of labor. 



One of the most common methods is the use of a large cork- 

 borer, or apple-corer, to cut a cylinder from the potato. This 

 cylinder of potato is divided diagonally, thus making two prep- 

 arations. Pieces of glass tubing are inserted into the thick ends 

 of the two pieces of potato, and they are placed into ordinary test- 

 tubes and sterilized. The pieces of glass tubing serve to support 

 the potatoes above the level of the condensation water, which al- 

 ways settles into the bottom of the tube. In some instances, 

 specially made culture tubes having a constriction near the bot- 



