TRANSACTIONS OF SECTION D. 541 
4. Report on the Occupation of a Table at the Zoological Station, 
Naples.—See Reports, p. 346. 
5. Report on the ‘ Index Animalium.’—See Reports, p. 347. 
6. Report on Experiments on the Development of the Frog. 
See Reports, p. 347. 
7. Report on Colour Physiology in Animals. 
See Reports, p. 349. 
8. Interim Report on the Effects of Sera and Antisera on the Development 
of the Sexual Cells.—See Reports, p. 350. 
9. Interim Report on Zoology Organisation.—See Reports, p. 350, 
10. Seventeenth Report on the Zoology of the Sandwich Islands. 
11. Joint Discussion with Section K on the Physical Basis of Inheritance. 
Opened by Professor Sypnzy J. Hickson, F.R.S. 
The theory that the chromosomes of the ovum and spermatozoon constitute 
the physical basis of hereditary characters appears to be accepted by many 
biologists, and there is a danger that it will become incorporated among the 
dogmas of our science unless opportunities are taken for ample discussion of the 
known facts of cytology that tell both against and in favour of the theory. 
The principal piece of evidence that is quoted in favour of the hypothesis is 
the experiment of Boveri (1889), which demonstrated that an enucleate ovum 
of one species fertilised by a spermatozoon of another species produced a larva 
with purely paternal characters. As confirmatory evidence of the theory there 
have been quoted (1) the constancy in the number of the chromosomes in the 
somatic cells, (2) the reduction to one half of the normal number of chromo- 
somes in the sexual cells, (8) the presence of similar heterogeneous chromosomes 
in the sexual cells of certain arthropods and their mutual relationships. 
If the theory is true it appears to be necessary to believe in the individuality 
of the chromosomes, that is to say, that the chromosomes seen at the poles of the 
spindle at the close of mitosis are individually the same chromosomes as those 
that are seen on the equator of the spindle at the next mitosis. 
If the theory is true it follows that the cytoplasm of the ovum and sper- 
matozoon plays no part in the transmission of hereditary characters. 
The principal difficulties at present in the way of accepting the theory are 
briefly as follows: Experiments in merogony have shown that an enucleate egg 
fertilised by a spermatozoon of another species of animal does not-always give rise 
to a larva with purely paternal characters. The evidence that in some animals 
the individuality of the chromosomes is not maintained, particularly in certain 
rhizopoda and infusoria among Protozoa and certain Coelentera, is convincing. 
In the tissues of most animals and plants there is no direct evidence that the 
individuality of the chromosomes is maintained between successive mitoses. 
If it is true that the cytoplasm of conjugating cells is not concerned with the 
transmission of hereditary characters, it is difficult to account for (a) the long 
