SECTIONAL TRANSACTIONS.—D. 491 
AFTERNOON. 
Dr. H. O. Butu.—The experimental study of conditioned responses in 
fishes (2.15). 
Dr. C. F. A. Pantin.—Nerves and nerve-nets in Invertebrates (3.0). 
Nervous action in the Invertebrates is often said to differ fundamentally 
from that in the Vertebrates. But in fact there appears to be only one 
important difference. Except in the Vertebrata, ‘ peripheral facilitation ’ 
is enormously developed, especially between nerve and muscle. That is, 
the first nervous impulse passes into few or none of the muscle fibres, while 
each succeeding impulse is increasingly successful in doing so. This is 
responsible for the varied muscular responses of the Crustacea, the Actinozoa 
and probably the Echinoderms. ‘The special properties of the nerve-net 
in the latter groups are due to facilitation. 
The natural responses of the Actinozoa are effected by well-defined 
muscles, which fall into two groups according to their relation to the nerve- 
net. In one the net acts as'a simple conducting unit from the site of the 
stimulus to the muscle ; facilitation occurs only between the nerve-net and 
the muscle. In a second group the nerve-net supplying the muscle is 
partly isolated from neighbouring regions of the net. Between these 
regions inter-neural facilitation takes place. This analysis throws much 
light on the nature of autonomy in the nerve-net and on the origin of polar 
conduction. A fairly complete picture ¢an be drawn of the Actinian 
nerve-net and of the manner in which it subserves the organism in its 
natural environment. 
Tuesday, September 12. 
Joint Discussion with Sections I (Physiology) and K (Botany), on 
Genetics :— 
Prof. J. S. Huxtey.—Physiological genetics (10.0). 
Prof. R. R. Gates, F.R.S.—The general nature of the gene concept 
(10.30). 
Dr. C. C. Hurst.—The significance of genetics in evolution (11.0). 
The science of genetics has advanced rapidly during the last decade. 
The mechanism of heredity and variation, which was unknown to Darwin, 
has been revealed to us by the microscope. Experiments show that mor- 
phological, physiological, and psychological characters are alike organised 
by sets of genes carried by the chromosomes of the cells. Consequently 
it is now possible to re-arrange the old indefinite Linnean species into 
definite genetical species which are experimentally determinable by their 
gene-chromosome complexes. ‘Thus taxonomy becomes an exact science 
and the genetical species provides a measurable unit of evolution. 
The gene is the unit and basis of life and progressive evolution can be 
traced from the monogenic species of Bacteriophage of molecular size to the 
polygenic species of the Primate Man carrying a genechromosome complex 
which produces a conceptual mind. The exercise of this in scientific 
research is rapidly bringing power and freedom to man by gaining more con- 
trol over nature and life. Experimental hybridisation of genetical species 
