Xll 



PRESIDIiNTIAL ADDRESS 



to be directly concerned in the vital activity of the cell. Proofs 

 of this were abundantly forthcoming. For instance, on many 

 ponds you will observe tangled masses of green slimy substance 

 known as spirogyra. When some of this is removed and 

 examine-J microscopically, it is found to consist of long filaments 

 consisting of cells united end to end, and through each cell mns 

 a beautiful spiral green band. If the contents of the cell are 

 examined through the opening of this spiral, the nucleus will be 

 observed, and passing to it from the walls of the cell are strands 

 of protoplasm. The nucleus gradually shifts its position and 

 traverses the cell, carrying with it the protoplasmic strands 

 Moreover, if the filaments are kept .inder observation for 

 some time, it will be found that at times two of them approach 

 each other and lie side by side. Then canals are put out by 

 the cells on one side and unite with those on the other, and the 

 contents of the cells on one side are poured through these into 

 the cells on the other. Then comes the significant fact • the 

 two nucleii approach each other and finally coalesce. A spore is 

 formed by the union of the contents of the two cells, and by the 

 coalescence of the two nucleii is formed the germinal nucleus of the 

 spore. Again, if we study -for an hour or two such an animalcule as 

 the vorticella-a minute infusor, just visible in the colonies of the 

 larger species to the naked eye, and freq.iently occurring in 

 ponds we find that each unit consists of a single cell, placed on a 

 corkscrew-hke stalk, which expands and contracts. Its structure 

 can be readily studied under the microscope, and the nucleus 

 will be at once detected. If one of the cells is kept under 

 examination for a sufficient time, the phenomenon of division 

 can be watched. After a period of active feeding and rapid 

 movement of its circlet of hair-like processes, or cilia, the latter 

 are drawn in, a cleft or groove appears at the top, the nucleus 

 elongates, and the cell gradually divides through the nucleus 

 into two complete cells, one-half of the nucleus remainina in 

 each. It is common, therefore, to find two cells on the same 

 stalk, the process not having progressed to the extent of a 

 separate stalk for each. But the essential point here is the 

 partition of the nucleus between the cells, which are formed as 

 the result of subdivision, and the inference which arises that the 

 nucleus is the centre of vital activity. That this inference is 

 correct has been demonstrated in a remarkable manner. A 

 lowly animalcule is cut in pieces under a dissecting microscope. 

 Some of the pieces are severed so as to include no part of the 

 nucleus, and others so as to contain portions of that singular 



