PRESIDENT’S ADDRESS. 4]] 
This view received powerful support from the experiments of 
Roux. Roux cut a segmenting frog’s ovum, consisting of two 
cells, into halves. Both halves continued to segment and produced 
hemi-embryos, which lacked one half of the body. ‘hat the 
potentialities of the cells of an embryo are certainly early differ- 
entiated must be conceded by all, but this differentiation would 
appear, from the observations of Hertwig, Pfluger, and Driesch, to 
occur later in the history of the segmenting ovum than Weismann 
imagined, 
These authors also succeeded in separating single blastomeres of 
segmenting ova, and found, in opposition to the results of Roux, 
that they developed into complete, though dwarfed larvee. 
From the results of Hertwig, segmentation in early stages 
appears quantitative rather than qualitative, and the earliest 
segmentation cells are, therefore, isodynamic. 
The general truth of Weismann’stheory must I think, beadmitted, 
but when he postulates from complexity of function, corresponding 
complexity of mechanical structure, and talks familiarly of ids, 
idants, determinants, and biophors !—my head swims, and I feel, 
also, that a too-continuous repetition of these terms occasions a 
liability to overlook their highly speculative nature. He also 
appears quite unjustified in choosing the nucleus, or a part only 
of the nucleus, as the vehicle for his hereditary mechanism. True, 
most interesting and suggestive behaviour has been observed on 
the part of the chromatin filaments prior to and during division ; 
but has not one’s attention been directed to this part of the whole 
cell by the accidental circumstance that it stains, or is otherwise 
easily made visible, whereas we are left mostly in the dark as to 
what is taking place in the remaining portion ? 
Whatever one’s opinion of the value of Weismann’s theory may 
be, one must realise the immense value of his work in stirring 
up controversy and research in this field, and especially for so 
forcibly pointing out that a great principle in heredity—namely, 
the transmission of acquired peculiarities—had been tacitly 
admitted with altogether insufficient credentials. The concep- 
tion of a germ possessed of such an infinitely complicated archi- 
tecture as is necessitated by Weismann’s theory does not attract 
me. It is, at the same time, too complex in detail, too simple in 
principle. 
Nevertheless, I fully realise the value of any consistent theory 
of heredity to provide pegs whereon to hang facts for the time-being 
in some sort of order, instead of their being littered about the 
journals of the whole civilised world. It provides biologists with a 
systematized wardrobe, the arrangement of which is easily acquired. 
In the mean time, they may continue to gather their facts by 
observation and experiment, for the purpose of formulating some 
general laws of heredity. 
