1892.] NEW-YORK MICROSCOPICAL SOCIETY. 15 



plants, commonly multiply by simple fission, and amongst the true 

 infusoria, or animalcules, the operation is so rapid that, in some 

 genera (as, for example, the vorticellae), one may witness within 

 an hour the complete bisection of a single vigorous creature into 

 two lively counterparts. The process in the plant-world is gene- 

 rally much slower, but it passes through essentially the same 

 steps and may be traced with equal clearness and certainty. In 

 fact, at their foundation all modes of reproduction are but forms 

 of fission, — the division of one into two or more, — and the ultimate 

 nature of the process is not changed by the fact that the resulting 

 two are often so dissimilar in size and other attributes that we 

 feel bound to regard one as the parent and the other as the 

 offspring. In other words, it is none the less fission because it 

 takes the form we call budding. 



I have a strong liking for the system which classifies this 

 whole matter under the two heads, continuous gemmation and 

 discontinuous gemmation, — the former covering all cases in which 

 the bud or fruit remains permanently attached to the parent 

 stock, and the latter those cases in which it is set free to shift for 

 itself. Examples of continuous gemmation are found among 

 those non-vascular algae which are nevertheless multicellular in 

 habit, as well as among those animals whose individuality is 

 wholly subordinated to a commensal mode of existence. Under 

 the first head we have such lowly plants as the net-like hydro- 

 dictyon, the thread-like spyrogyra, and the chain-like diatoms ; 

 under the second we find all such perplexing creatures as the 

 sponges, corals, and zoophytes. 



Continuous gemmation gives rise to very interesting and com- 

 plicated relations which involve another insoluble biological puz- 

 zle, — as to what constitutes an individual. When one regards 

 the cell-units, with their circumscribed and apparently complete 

 cell-functions, he is disposed to credit them with the real indi- 

 viduality ; but when he looks to the mutual interdependence 

 which usually exists between the cells which retain a physical 

 connection with one another, he inclines to expand the idea so as 

 to include all the members of any communal aggregation, if he 

 does not stretch it still further, as some authors do, so as to cover 

 all the products of fission or gemmation within a continuous se- 

 ries, whether remaining unitfed or not. In such cases, however 



