514 TRANSACTIONS OF SECTION D. 
of the tube, where, having ascertained by an exquisite sense of touch the inoment 
when an exact fit has been obtained, it is fixed by the cement which is poured 
out by the underlying cement-gland. 
15. The Influence of Osmotic Pressure on the Regeneration of Gunda 
ulve. By Miss Dororuy Jorpan Luoyp, B.Sc. 
This work was carried out in the laboratory of the Marine Biological 
Association at Plymouth during the summers of 1912 and 1913. 
G. ulvew is a small triclad found in great numbers at Plymouth. It lives 
between the tide marks and near the borders of a small stream. The worms 
used in the experiments were all of the same size (5°55 mms. approx.). They 
were cut transversely into two equal halves. Only posterior regeneration is 
considered in this paper. The artificial waters used were made up by mixing 
known volumes of sea-water and distilled water, or, for the higher values, by 
mixing known volumes of sea-water and of a 23 molecular solution of sodium 
chloride. The osmotic pressure for any given salinity of sea-water was taken 
from Krummel’s ‘ Handbuch der Ozeanographie.’ 
The following points were noticed :— 
1. Whole worms can live indefinitely in water having an osmotic pressure 
between 2 and 33 atmospheres. 
2. Regulation of an anterior half resulting in the production of a complete 
worm takes 50 days (at 15° C.) in water having an osmotic pressure between 
15 and 22°5 atmospheres. (Osmotic pressure of sea-water=22°5 atmospheres). 
3. Lowering the osmotic pressure below 15 atmospheres retards the rate of 
regulation proportionately. Below five atmospheres pressure no regulation occurs. 
4, Raising the osmotic pressure above 22'5 atmospheres retards the rate of 
regulation. Above 30 atmospheres no regulation occurs. 
5. The new posterior region is formed by the migration of large numbers of 
parenchyma cells to the region of the wound, where they aggregate and build up 
the new organs. Inhibition of regulation seems due to some factor which checks 
the migration of the parenchyma cells. 
6. In the worms showing retarded regulation irregularities in the mitotic 
divisions of the parenchyma cells have been noticed. 
FRIDAY, SEPTEMBER 12. 
The following Papers were read :— 
1. The Classification of the Pierines. By Sir G. Kenricx. 
2. The Heredity of Melanism in Lepidoptera. By W. Bowater, B.D.S. 
Apparently the term melanism as applied to lepidoptera should be restricted 
to the substitution or increase of black on the wings or body, or both, at the 
expense of some other colour, but any darkening of the ground colour, although 
not black, has been included in a general way, although strictly the term 
melanochroism should be applied to the latter. 
The list of species in which melanic specimens have been recorded is quite 
formidable, but many are merely cases of melanochroism. 
The exemplary and very extensive experiments made on the London (dark) 
and French (light) forms of Acidalia virgularia by Messrs. Prout and Bacot * 
proved that these varieties are not Mendelian forms of the species, but Mr. 
W. B. Alexander demonstrated that the speckling of virgularia is dominant to 
non-speckling. : 
Experiments by Mr. Buckley on Acidalia contiguaria show that the dark form 
is dominant. 
Messrs. Prout and Bacot found in another moth, Triphana (Agrostis) comes, 
1 Proc. Roy. Soc. Lond. 1909. 
