726 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
Tlie entire mantle may be said to be covered with a cuticular shield, 
which outside the region of the shell bears calcareous spines. As the 
articulamentum alone is comparable with the ordinary Gastropod 
shell, and as the cutieula covers all, it seems certain that the cuticula 
is phylogenetically the more primitive. Herr Blumrich sketches the 
possible evolution of the shells from spines, and of the aesthetes from 
specialized papillae of the mantle, but we cannot enter into the de- 
tailed results of his investigations. In a preface, Prof. Hatschek dis- 
cusses the general importance of this study, which has obvious bearings 
on the question of the relationship between the Chitonidae and the 
Aplacophora. Pelseneer’s conclusion is corroborated that Chiton is 
nearer the primitive type than Chitonellus , and that Neomenia and 
Chsetoderma are degenerate forms. 
5. Lamellibrancliiata. 
The Free-swimming Larva of Dreissena .* — Prof. F. Blochmann 
has found this larva, which has strangely escaped earlier discovery. It 
swims freely and seems to be abundant in the Ober-Warnow at Bostock, 
where Dreissena has firmly established itself. The transparent ova are 
extruded in clumps at the bottom of the stream ; only the larvae rise in 
the water. Dr. E. Korschelt has also found the larvae, and will study 
their development. 
Circulation in Arca.f — Dr. P. Frangois has a note on the circulatory 
apparatus of Area barbata (?). The auricles are almost triangular with 
the bases widely separated, so that, superficially, they look like two 
hearts ; the ventricle is much reduced, and forms a sort of aortic bulb ; 
the aorta, on leaving the heart, passes forwards, and to the right ; it 
gives rise, on its left side, to three or four secondary trunks. The 
blood is like that of Vertebrates, coloured with a little water. This 
colour is due to a large number of very flat elliptical corpuscles which 
are all about 21 /x across. These observations have been verified on 
A. pilosci (?). 
Molluscoida, 
a. Tunicata. 
Tunicata.J — Prof. W. A. Herdman has published a revised classifi- 
cation of the Tunicata, in which he gives definitions of the orders, sub- 
orders, families, sub-families, and genera, with analytical keys to the 
species. He now takes a more extended view of the group than he was able 
to take in his c Challenger ’ Beports. Among the Cynthiinm there are the 
new genera Bhabdocynthia , which is established for the reception of 
those species which are provided with needle-like or rodlike spicules of 
carbonate of lime scattered through their tissues, and Forbesella , for 
C. tessellata of Forbes, which is remarkable for having only four folds 
on each side of the branchial sac. Among the Clavelinidse Bho- 
palopsis , Podoclavella, and Stereoclavella are new generic groups which 
material recently acquired by the author has led him to establish. The 
* Biol. Centralbl., xi. (1891) pp. 47G-8. 
t Areh. Zool. Exper. et Gen., ix. (1891) pp. 229-31 (1 fig.). 
+ Journ. Linn. Soc. Lond., xxiii. (1891) pp. 558-652. 
