448 SECTIONAL TRANSACTIONS.—D. 
2nd edit., Chap. XV.). The problem to be explained is the sexual limitation 
of inheritance, and that we know now is due to the action of the sexual hormones. 
At the meeting of the Association last year Mr. J. 8. Huxley discussed the 
question of time-relations in amphibian metamorphosis, especially with regard 
to the discovery that the metamorphosis is to a great degree influenced by the 
internal secretion of the thyroid. Administration of thyroid hastens meta- 
morphosis in the frog, causes it in the Axolotl, but fails to produce it in 
Perennibranchiates such as Necturus. ‘The question to be considered is the 
relation of these facts to the old problem of metamorphosis as a recapitulation 
of successive stages of evolution. It is this problem which is being overlooked 
and forgotten. 
On the other hand, we have the discoveries of the geneticists, especially the 
occurrence and nature of mutations. These are of quite a different character 
from the changes indicated by recapitulation, and a careful comparison will 
show that mutations like those observed could never, for example, have 
resulted in the evolution of terrestrial from aquatic vertebrates. 
None of the recent discoveries throws any new light on the question of the 
origin of adaptations, except one—namely, that the sexual limitation of inherit- 
ance is due to the influence of the sexual hormones. 
5. Mr. H. R. Hewer.—-Colour Changes in the Common Frog. 
1. A hormone from the posterior lobe of the pituitary (pars intermedia) has 
been established as the chief factor (central control) of coiour change in the 
common frog. 
2. The effects of environmental stimuli have been determined to a certain 
extent. 
Low temperatures, moisture, and black background tend to produce darkening 
of the skin. 
Medium to high temperatures, dry surroundings, and white background tend 
to produce pallor. : 
The effect of light and darkness is obscured by the effects of background, 
but it would seem that the former tends to produce pallor and the latter 
darkening of the skin. 
3. The receptors ot these stimuli are discussed. The only ones definitely 
known are those for background—namely, eyes and some kind of receptor in ~ 
the skin. 
4. Evidence has been brought forward to show that the stimuli transmitted — 
from the eyes to the pituitary are inhibitory in nature, and probably pass by — 
way of the parasympathetic nervous system. 
5. It is stated that the weight of the evidence goes to show that the dermal — 
melanophores ‘ expand’ and ‘ contract’ by means of movements of the granules i 
alone. 
6. No evidence has been brought forward to show how the pituitary hormone 
brings this about. 
6. Mr. Junian S. Huxtey.—Lecture on The Physiology of Develop- 
ment in the Frog. 
a gee ee 
Friday, September 14. 
7. Prof. James Jounstone.—Rhythmic Change in the Plankton. 
This paper is an account of the results of a series of plankton hauls made | 
by Sir William Herdman in Port Erin Bay during the years 1907-1920. The 
catches have been worked through by Mr. Andrew Scott and the numbers” 
of the larger organisms have been estimated in each example. These quanti- 
tative results are tabulated and means for the series of fourteen years are 
calculated. There is a very clear seasonal change in the case of each organism, 
and this repeats itself from year to year throughout its period. The time of 
occurrence of the maximum of abundance may vary, throughout the series, by 
a month or more, and there is also a variation in the actual quantities of each | 
organism taken. There may be no similarity, even in the case of closely related 
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