302 
SUMMARY OF CURRENT RESEARCHES RELATING- TO 
Purpura lapillus is also busy at work, sawing out tbe Balani from their 
shells. The author thinks that the mantle tentacles, of which as many 
as a hundred may he present on a Limpet, help in the locality sense. For 
the homing habit these tentacles appear to be of two kinds, some longer 
and some shorter. The fact that Heleion pellucidum also possesses the 
homing faculty appears to be new to general knowledge. The object of 
homing seems to be protection from the assaults of the incoming or out- 
going tide. There is no danger when the objects are completely covered 
or uncovered. The force with which Limpets adhere is illustrated by 
the fact that five small Limpets at Aberystwyth were quite uninjured by 
the terrible gale and high sea of December 21 and 22 last. The much 
thinner shell of Heleion is explained by the sheltered position of its 
home. The author is inclined to adopt the suggestion of Prof. Michael 
Foster, that the adhesive power of the Limpet is due to the adhesion 
being like that between two smooth glass surfaces brought very close 
together. Tlie muscular foot is, so to speak, rolled out on the rock, with 
which it is thus brought into close contact. 
5. Lamellibrancliiata. 
Mode of Fixation of Lamellibranchs by their Byssus.* — M. L. 
Boutan has made experiments with Area tetragona , where the byssus is 
compact and is of enormous size in proportion to the whole mass of the 
animal. His experiments show that adult Arcse are compelled, if their 
attachment is broken, to refix themselves by first getting rid of all the 
old byssus and by secreting a new one, whereas young Arcse can fix 
themselves by the aid of the old organ. These apparently contradictory 
facts are explained by a study of the structure of the byssus. The 
byssus secreted between the glandular lamellae is formed in Area by a 
series of lamellae fitted into one another. The matter secreted in the 
fluid state is injected between the lamellae, and protected by the foot 
against the action of water. When the secreted matter can make its 
way out it can re-establish the attachment of the byssus, as is the case 
with the young forms. When, on the other hand, the byssus has become 
compact in its upper part this injection is impossible. Further 
observations are promised. 
Bryozoa. 
Embryonic Fission in Lichenopora.f — Mr. S. F. Harmer reminds 
the student that he has already shown that the primary embryo of Grisia 
gives rise to numerous larvae by a constantly repeated process of 
embryonic fission, and he has suggested that this method of development 
will be found to be characteristic of cyclostomatous Polyzoa in general. 
The observations he has recently been able to make on L. verrucaria 
from the coast of Norway, have enabled him to prove the occurrence of 
embryonic fission in a second genus of Cyclostoma, although the details 
are remarkably different from those of Grisia. The author gives a brief 
preliminary account of his observations, and concludes that the following 
results may be deduced from them. The ovicell is not altogether 
* Comptes Rendus, cxx. (1895) pp. 208-10. 
f Proc. Roy. Soc. London, Ivii. (1895) pp. 188-92. 
