914 
Proceedings of the Royal Society 
sooner or later checked by the preponderance of katabolism, and 
that the most frequent alternative is the restoration of the balance by 
cell-division. To this 
Continuous Growth. 
physiological necessity, 
Continuous Cell-H n . 
Fig. 2. 
then, is referable (with 
Discontinuous Growth or 
Reproduction. 
Spencer) the origin of discontinuous growth or asexual reproduction. 
Budding, simple-division, and spore-formation like continuous cell- 
division, are simply different forms of the necessary separation which 
must occur at the limit of growth, if the continuity of life is to be pre- 
served. Like continuous cell-division, asexual reproduction occurs 
when waste or katabolic processes are in the ascendant. But what 
holds true in the growth of the individual cell, is valid also in regard 
to the aggregate. There, too, a limit of growth must eventually be 
reached, when discontinuous growth in some form becomes inevit- 
able. The essential difference is simply that at first in the uni- 
cellular individual the disintegration and reintegration entirely 
exhaust the organism and conclude its individual existence, while in 
higher forms the process becomes more and more localised. 
(b) Sexual Reproduction : Phylogenetic Evolution. — Turning now 
to the connection between asexual and sexual reproduction, it will 
be convenient, in the first place, to resume the facts of the phylo- 
genetic evolution, and then to interpret these physiologically. The 
clear morphological account given by Vines (see his discussion of 
“ Reproduction — Vegetable,” Ency. Brit.) may be taken as a basis. 
(1) A simple protophy tic alga like Protococcus usually exhibits a per- 
fectly continuous asexual cycle, in which the cell divides into a number 
of equal spores which come to rest and develop to the normal size. 
A hint of incipient differentiation appears in the occasional division 
