ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
585 
which forms numerous folds at the edge of the shell was destroyed before 
the ablation of the calcareous part. In all cases this epidermis was 
renewed ; in animals preserved in their normal medium it had all its 
original characters ; it was covered on its outer side by crystals formed 
of a calcareous but not carbonated substance ; the crystals appear to be 
a product of the secretion of the elongated epithelial cells near which 
they are found, and appear to play the part of reserve-materials. In 
the animals kept in non-calciferous water there were young crystals, but 
they are less regular and not so numerous ; the presence of these few 
crystals is easily explained ; the shell of the animal after four months’ 
stay in the water had become completely transparent and so soft that, 
though still calcareous, it could be folded under the fingers like an 
elastic membrane. 
In all the specimens examined there had been a secretion of a 
substance destined to close the wound made on the shell. This layer was 
formed of several organized membranes, placed on one another, arising 
at some millimetres from the edge of the wound and all around it. At 
its surface and between the membranes which form it, the calcareous 
matter takes on very various forms. Rhombohedra, radiated crystals, 
or crystalline plates were all seen ; but in the animals which were 
preserved in the chalkless water there were no crystals of any kind. 
The pallial epithelium was led by the necessity of an active secretion 
to undergo profound modification. The cells are greatly elongated and 
provided with a large oval nucleus in which are one or two highly 
refractive nucleoli ; the protoplasm of the outer part of the cell is very 
granular and becomes stained green with methylene ; it is, in fact, 
identical in form and reactions with the glandular epithelia of the fold of 
the mantle-lobe and of the dorsal region. 
The author concludes that these observations show that the shell of 
these animals is a secretion-product of the mantle, that the earliest stage 
of the test is always a purely organic formation, and that the lime which 
strengthens the shell is obtained from the surrounding medium. 
Molluscoida. 
y. Brachiopoda. 
Stratigraphical Distribution of Deep-Sea Brachiopods.* — MM. P. 
Fischer and D. P. Oehlert report that the expeditions of the ‘ Travailleur’ 
and £ Talisman ’ dredged sixteen species of deep-sea Brachiopods. 
Thirteen of these have been found in the marine pliocene deposits of 
Sicily and Calabria; since the period of these deposits these species 
have become extinct in the Mediterranean while almost identical forms 
to them have been perpetuated in the Atlantic; three other species 
appear to be in course of extinction, as isolate I valves were alone 
dredged from the Mediterranean, while the forms are still abundant in 
the Atlantic. 
The authors ask why there should be this tendency to the disappear- 
ance of abyssal forms from the Mediterranean, and correlate it with the 
gradual heating of that sea, which is, as compared to the Atlantic, 
closed. These considerations seemed to confirm the hypothesis that the 
* Comptes Rendus, cxi. (1890) pp. 247-9. 
