3i6 Report of the Microscopical Section. [Sess. 



of great problems which these minute organisms present to the 

 thoughtful naturalist. There are no objects more beautiful 

 than the Protozoa, when observed under the microscope in the 

 living state, — and it is the ideal of the field naturalist to 

 study the living organism first and chiefly, and afterwards to 

 dissect it, or to employ methods of microscopical examination 

 to get more knowledge as to how the living machine works. 

 The living protozoan — say a vorticella, a paramcecium, or a 

 stentor — is so transparently beautiful that no technical skill 

 in the preparation of permanent objects does more than produce 

 a well-preserved mummy of it. To-night we have got together 

 a few living Protozoa — not so many as I should have liked. 

 Preserved specimens, to show cell structure, muscular changes, 

 and the like, are better reserved for special evenings. 



As I have just indicated, there are many very interesting 

 problems presented to us by the Protozoa. The Protozoa are 

 mostly invisible to the naked eye : some are not. For ex- 

 ample, the little organism which occurs in such enormous 

 numbers as to make our seas luminous during the nights of 

 autumn — the noctiluca — is quite visible, being about as big 

 as a small pin-head. Notwithstanding their minuteness, and 

 consisting as they do of a single cell, the Protozoa perform 

 the vital functions of animals built up of many cells. They 

 are generalised single cells. The cells of multicellular animals 

 are specialised cells : muscle cells contract par excellence, kidney 

 cells secrete, and so on ; but in a protozoan the single cell 

 does all these things, hence it is said to be generalised. Still, 

 generalised though it is, it may have a great deal of intra- 

 cellular structure, — structure within the cell itself. For 

 example, in getting food an amoeba is like a piece of fluid 

 jelly : it seems to send out false feet anywhere, and so gets 

 hold of another and smaller object than itself, such as a 

 diatom, which is surrounded and then digested. But the 

 false feet may be confined to one end of the animal, as in the 

 shelled rhizopods (Difflugia or Arcella). For the higher 

 Protozoa, flagella or cilia in fixed positions take the place of 

 vague false feet in obtaining food. 



Then in the higher Protozoa there may be some portion 

 of the protoplasm more sensitive to external stimuli than 

 the rest — e.g., the so-called " eye spots " in Euglena. There 



