354 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
the Lamell i branch iata. He has certainly observed it in Yoldia, Pecten, 
Mytilus , Anodon, and Yeitus, and probably in Area aud Ostrea. 
There appears to be an almost constant correlation between the 
aborted or absent foot and a thick mantle with no large blood-spaces, 
and also between a fully-developed locomotor foot and a mantle con- 
sisting mainly of immense blood-spaces. Very large mantle-chambers 
appear to be characteristic of those forms which are most active. When, 
as in the oyster, the breaking down of tissues and the need of aeration 
is reduced to a minimum, there is a very small branchial chamber. The 
author suggests that the plate-gill is homologous not only with the 
descending limb of a filament, as Mitsukuri suggests, but with both 
ascending and descending limbs, for the former is merely a continuation 
of the latter. 
Molluscoida. 
a. Tunicata. 
Development of Vibratile Organ of Compound Ascidians.* — M. A. 
Pizon has studied the development of the so-called vibratile organ 
(olfactory organ of Hancock) in a number of difierent Compound 
Ascidians. He finds that it commences as a blind tube formed by a 
diverticulum of the primitive endodermic vesicle, and that it opens 
secondarily into the branchial vesicle, while its hinder part undergoes 
a more or less rapid atrophy. This is contrary to the view of Van 
Beneden and Julin, who describe it as being due to a buccal invagina- 
tion, and consequently homologize it with the hypophysis of Vertebrates. 
Owing to its early appearance, M. Pizon thinks that we ought to regard 
it as eminently an ancestral organ, which had probably a very important 
function in the primitive forms of Tunicata. The variations which it 
exhibits during the development of an ascidiozooid, its progressive 
atrophy and its almost complete disappearance in the Didemnidre, shows 
that, at the present day, it performs no important function. 
/3. Bryozoa. 
General History of Marine Polyzoa.j — The Eev. T. Hincks con- 
tinues his ‘ Appendix ’ to his ‘ Contributions towards a General History 
of the Marine Polyzoa,’ and describes several new forms; the only new 
genus is Eeteroecium, one of the Membraniporidse, which is remarkable in 
that the true external ocecium is not, as is usual, an appendage of the 
zooecium, but an integral part of it. 
y. Brachiopoda- 
Brachiopoda of the ‘ Travailleur ’ and ‘Talisman’ Expeditions.! 
— MM. P. Fischer and D. P. Oehlort report on the sixteen species of 
Brachiopoda obtained in four dredging expeditions by the above-men- 
tioned French exploring vessels. Of these species only two were found 
to be undescribed. The authors discuss the geographical distribution 
of the species, and the lessons to be learnt from them ; to the most 
important of these we have already § called attention. 
* Comptes Rendus, cxiv. (1892) pp. 237-9. 
+ Ann. and Mag. Nat. Hist., ix. (1892) pp. 327-34. 
J ‘ Expeditions Scientifiques du Travailleur et du Talisman . . . Bracliiopodes,’ 
4to, Paris, 1891, 140 pp. (8 pis.). § See this Journal, 1890, p. 585. 
