TRANSACTIONS OP SECTION D. 631 



B. After treatment with butyric acid, faSowd by hypertonic salt solution 

 (Loeb's improved method). 



8. The interval between treatment with butyric acid and the hypertonic salt 

 solution is characterised by the membrane-formation and an alteration in the 

 staining properties of the nucleolus. These changes are accompanied by the 

 appearance of a clear perinuclear zone, as described above (3). 



9. During the treatment with hypertonic salt solution there is a slight increase 

 in the size of the nucleus. 



10. After transference of the eggs back into normal sea-water the perinuclear 

 zone still further develops, and is followed by growth of the nucleus. 



11. A typical cleavage aster is formed by the division of a centrosome, that 

 first appears on the nuclear membrane. 



12. A varying number of cytasters may appear. If excessively developed 

 they interfere with the normal division of the cell, and multipolar spindles are 

 funned. The cy tasters are only developed in eggs that have remained too long 

 in the hypertonic solution. 



13. The chromatin breaks up into eighteen chromosomes, which is halt th" 

 number occurring in normally fertilised eggs. The reduced number of chromo- 

 somes (eighteen) persists in the cells of the parthenogenetic larv;e at least as far 

 as the free-swimming blastula. and beyond this stage it is impossible to count 

 them, owing to the small size of the cells. 



In conclusion, the suggestion is offered that the known facts of artificial 

 parthenogenesis may be competent to explain the origin of cancer. 



The following Papers and Reports were then read in Section D : — 



1. Note on the Biology of Teleost and Elasmobranch Eggs. 

 By W.J. Dakin, D.Sc. 



Observations made by the author two years ago confirmed the results of 

 experiments made by Botazzi and others which indicated that the osmotic pressure 

 and salinity of the blood of marine teleosts was very different from that of the 

 external medium in which they lived, but showed, however, that the osmotic 

 pressure and salinity of the blood was affected by changes in the salinity of the 

 water. The blood of the eel has a lower osmotic pressure in fresh water than in 

 the sea. The blood of freshwater fishes is less saline than that of marine fishes. 



The osmotic pressure of the blood of elasmobranchs is almost identical with 

 that of the sea water in which they live. 



Does the egg-contents or body-contents of young teleost larvae bear the same 

 relation to the sea water as the blood of the adult fish? 



Experiments have shown that the specific gravity of plaice eggs can be 

 altered by varying the salinity of the water in which they are living. The egg- 

 contents are therefore not altogether independent of the sea water. At the same 

 time, by determinations of the freezing-point, and consequently direct measure- 

 ments of the osmotic pressure of the egg-contents, it was shown that the salinity 

 and osmotic pressure was very much less than that of the medium in which th-3 

 eggs were living and about the same as that of the blood of the adult fish. 



There is therefore an equilibrium between the sea water and the egg-contents 

 which does not consist in an equality of osmotic pressures; and while both 

 osmotic pressures are very different, a change in that of the water produces a 

 small but definite change in that of the egg-contents. 



Death of the eggs destroys the conditions under which this equilibrium i.s sus- 

 tained, and the egg-contents increase in salinity by reason of the influence of the 

 surrounding sea water. A corresponding increase m specific gravity takes place, 

 and the egg is no longer able to float. 



The osmotic pressure of elasmobranch eggs i.s very different from that of 

 teleost eggs, though both may be living in water of the same salinity. The relation 

 existing between the egg-contents of dog-fish eggs and the, water is the same as 

 that between the blood of the adult fish and the medium in which they live. 



