492 SECTIONAL TRANSACTIONS.—D. 
and bombardment of their germ-cells by X-rays have already created 
numbers of new species and forms, and the time is at hand when natural 
selection can be replaced by human selection and man himself will be 
able to control evolution and in a large measure determine his own destiny. 
Dr. K. B. BLackBurN.—The synthesis of species (11.20). 
Recently new true breeding species have been produced experimentally 
by crossing two other species and these do not, as a rule, produce fertile 
offspring when backcrossed with their parents. The secret of their origin 
is revealed by their cytology. Lack of fertility in a species hybrid is often 
due to incompatibility of the chromosomes of the parents, but most of these 
new species have been produced by a doubling of the complete complement 
of the hybrid, thereby producing two equivalent sets to pair at meiosis. 
This gives the pure breeding character which marks them off from the 
hybrid swarms produced from crosses which are more or less fertile in the 
first instance. Such forms have been produced by crossing species (Primula 
Kewensis, Nicotiana digluta, Crepis artificialis) or even genera (Raphano- 
Brassica, Atgilotricum). Similar naturally occurring forms have now been 
recognised (Rosa Wilsoni, Spartina Townsendii), but the crowning piece of 
evidence for this as a natural method of species building is the production 
by Miintzing of plants indistinguishable from the common hemp-nettle 
(Galeopsis tetrahit) by crossing two quite distinct species, G. pubescens and 
G. speciosa. 
Dr. IRENE Manton.—The analysis of species (11.40). 
Col. C. J. Bonn, C.M.G.—Hormones and genetics (12.0). 
The importance to physiology of the particulate discontinuous nature of 
the heredity process, as established by Mendel. 
Diabetes a familial disease ; the pancreatic defect on which the disease 
depends is heritable. ‘Treatment with insulin ameliorates symptoms, but 
does not remove the defect. Effect of this on racial welfare. 
The evidence derived from a study of binovular twins, one of which may 
be a Cretin, or achondroplastic dwarf, and the other normal, throws light 
on the genetic factors concerned in thyroid and pituitary abnormality. 
Tissue cell susceptibility to hormonic influences may vary on the two 
sides of the body. Examples. The gynandromorphic pheasant. Asym- 
metrical spur development in hens. Asymmetric polydactyly in fowls. 
Gynandromorphism in insects. 
Acquired immunity and genetics. The immunity reaction in bacterial 
or coccal infections compared with that in virus diseases. ‘The influence 
of size of the infecting agent on the permanence of the reaction. If cell 
descendants (not offspring) are to remain immune, the nuclear heredity 
mechanism of the somatic cell must be concerned in the reaction. 
GENERAL DIscussION (12.20). (Prof. F. A. E. Crew; Dr. E. Asupy; 
Mr. J. T. CunnrincHAM; Mrs. C. B. 5. Hopson.) 
AFTERNOON. 
Mr. Micuart GraHaM.—Prediction of North Sea cod fisheries (2.15). 
It is known that fluctuations in the yield of certain fisheries, e.g. herring, 
plaice and cod, in the North Sea are largely determined by the degree of 
