321 
From the evidence afforded by the dissection of the Hartebeest and 
Nylghau, the conclusion must be drawn that in these Antilopidse 
the thymus is a permanent gland ; for there could be no doubt but 
that both these animals had reached the adult period of life, and 
even acquired a considerable age, — their large size, and the worn 
appearance of the teeth rendered this sufficiently manifest. So far, 
then, as regards these animals, the thymus must be looked upon as 
possessing a more enduring function than has hitherto been ascribed 
to it in the economy, — not disappearing or altogether degenerating 
in the early period of extra-uterine life, but persisting even in the 
adult animal. The paper concluded by some remarks upon the 
thyroid and thymus glands in the human subject. 
5. Notice on the Boring of the Pholadidae. By Alexander 
Bryson, Esq., President of the Royal Physical Society. 
In this communication the author referred to the various theories 
advanced to account for the boring of the Pholadidae in rocks. 
The first hypothesis, which supposes that the molluscs perforate 
by means of the rotation of the valves acting as augers, he disproved 
by exhibiting old individuals of the Pholus crispata with the den- 
tated costae as sharp as in any young specimen. That these animals 
bore by silicious particles secreted by the foot, as suggested by Mr 
Hancock, has been disproved by microscopic observation ; and that 
currents of water set in motion by vibratile cilia, seemed also insuf- 
ficient to account for the phenomenon. 
Another theory supposes that an acid is secreted by the foot, 
capable of dissolving the rock. 
This the author showed was not tenable, as the strongest Nord- 
hausen sulphuric acid fails to dissolve aluminous shales and Silurian 
slates ; and also that any such acid secretion would act more readily 
on the valves themselves. From many experiments on the cutting 
of hard silicious substances, the author found that the softer the 
substance was in which the cutting material was impacted, the 
greater the amount of the work done. He was thus led to the con’ 
elusion that the Pholadidse bore with the strong muscular foot alone, 
and that they obtain the silica from the waves or the arenaceous 
rocks in which they are found ; and hence there is no necessity for 
either an acid or silicious secretion. That the foot was the boring 
