1892.] THE MICROSC(3PE. 213 



natural descendants of prior forms. This idea has long been 

 struggling for existence in the world of beliefs, and cannot yet be 

 said to have gained a permanent place among the concepts of the 

 laity, though it is fully accepted by most professed biologists. 

 Looked at collectively the different kinds of animals appear to be 

 serial ; that is, they are not isolated and unlike, but are more or 

 less closely similar. The grades of similarity are somewhat par- 

 allel in different series. The groups that have been formed by the 

 study of animals includes phyla the most comprehensive and 

 classes, orders, ftnililies, genera, species, and varieties, named in 

 their lessening order. Each of these groups has a name and very 

 often the name we use in speaking of an animal is the name of its 

 order or class, not of its exact genus or species. Thus we speak 

 of the moth or fly or bee. In this way the same animal may be 

 called by several different appellations, and we may speak of the 

 gray squirrel as such or as a sciuroid, rodent, mammal, vertebrate 

 animal or even living tiling. We are thinking of different pecu- 

 liarities in each case as we use the various names of the squirrel 

 as representing those characters. 



The fact that the correlated groups are serial among themselves 

 and also stand in relation to other series of groups is an easily 

 demonstrated fact and will appear at once as we examine the pro- 

 tozoa. The present article will be an attempt in the limited space 

 available for the purpose to set forth the classes and orders of phy- 

 lum and to examine it biologically for the purpose of discovering, 

 if possible, the serial arrangement of its members and an explana-. 

 tion of the serial arrangement in biological terms. 



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 they be changes born in a bodv 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. I. Amoeba proteus ; 2. A. radiosa ; 3. formation; 16 Peridinium uberrimum; 17. 



A. villosa; 4. A. polypodia in act of division; Noctiluca miliaris ; 18, 19, 20. Codosiga um- 



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



cuneat ; 7. Actinospherium 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 1 



