4 
W. H. Lang. 
and many of the deductions that go to form the hypothesis can be 
found in the works of one or other of the authors named. The 
facts are indeed matters of common knowledge, and repeated 
reference to the more or less real similarity of the views taken 
here to those already expressed by other investigators would prevent 
a brief and clear statement being made. It seems better to simply 
state for what it is worth the view of alternation to which I am 
led. 
It is necessary to start with some general considerations on 
the nature of ontogeny, but we can avoid entering into the details 
of particular hypotheses of heredity. The general view of the 
organism and of its development from the germ-cell, which we are 
practically forced to take in the case of plants, is that all the cells 
resulting from the division of a germ-cell are potentially similar, 
and any one of them might reproduce the organism. The pre¬ 
valence of vegetative reproduction, which, even in highly complex 
organisms, may start from a single somatic cell, indicates this. 
The development of the body of an organism from the germ-cell is 
regarded as due (a) to the properties of the germ-cell and ( b ) to 
the conditions under which the germ-cell develops. The conditions 
of development in the case of complex multicellular bodies are 
partly external and partly internal, the latter including the important 
factors of correlation and of the influence of one stage in the 
ontogeny upon the succeeding one. We thus arrive at the concept 
of a specific cell corresponding to each specific form, to which 
under normal conditions it gives rise. 
In organisms without any alternation of generations there is 
only one type of body, 1 and any germ-cell, whether sexually or 
asexually produced, can be regarded as a specific cell with the 
power of giving rise under the proper conditions to a new indi¬ 
vidual like the parent. We have, however, to apply the concept of 
a specific cell to organisms with a definite alternation of 
generations. In these we meet twice in the life-cycle with a germ¬ 
cell, i.e. a cell capable of developing into an organism. These two 
germ-cells are the spore and the fertilised egg. The result of 
development of these two cells may be closely similar or widely 
different. The question at once presents itself, how are we to 
regard the ontogeny in these cases, and what do we understand by 
the specific cell of such an organism ? 
Recent work has shown that in certain Algae ( Dictyotn , Poly- 
1 The word “ body ” is here used to denote the vegetative organs 
of an organism, or of either generation of an organism, in 
contrast to the reproductive organs. 
