ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
329 
Structure and Growth of Calcareous Test of Balanus.* — M. A. 
Gruvel divides the test of Balanus into the wall and the base ; he finds 
that the test contains histological elements which disappear on decalci- 
fication, and that it is difficult to grind down sections sufficiently thin 
to allow of the easy study of these elements. By a method which he 
does not now describe the author has been able to make more complete 
researches. The wall of the test may be found to consist of three parts ; 
there is an internal portion produced by the mantle, an external part 
secreted by test-glands, and a third part formed by calcified columns. 
The innermost part is divisible into three layers ; an internal 
structureless layer, which is traversed by numerous small canals, which 
pass to the base of as many small setae which are perforated at their 
extremity, are disposed in parallel rows, and have the liquid of the 
general cavity circulating in them. This layer is what Darwin called 
the opercular membrane, and, in consequence of their function, the 
author proposes to call the setae respiratory. Between and outside 
these rows there is a true epithelium, formed of irregular polygonal 
cells, with large nuclei. More internally there is a series of concentric 
layers formed of a structureless transparent membrane, marked by 
irregular perforations throughout its whole extent. 
The second part exhibits, in a non-decalcified section, true calcareous 
glands, set at regular intervals, the excretory canal of which passes 
directly to the exterior ; the more early formed glands are often com- 
pletely calcified, when there are formed externally to them young glands 
which generally make use of the excretory canal of their predecessor. 
The cellular structure can best be studied in the young glands ; in them 
there may be seen an epithelium formed of flattened cells, and leaving in 
the midst of the cul-de-sac a free space which is often filled with granu- 
lations. These glands disappear completely when the wail is decalcified, 
and their impression only is seen on the decalcified intermediate tissue. 
The outermost layer is formed by a delicate cuticle, which is irregu- 
larly folded, and carries hairs set in parallel rows in which all kinds of 
vegetative growths are developed. The calcified columns occupy the 
whole height of the wall, and consist of a concentric series of layers of 
a structureless dotted membrane, absolutely the same as that in the 
inner portion of the first pair. Between the concentric layers there are 
numerous small cells, completely enclosed in a thick black pigment. In 
their upper part these columns or columellae are solid, but in the 
lower part there is a central cavity which contains a large number of 
fat-cells, with endothelial cells in concentric rows. The base is formed 
of several superposed layers. 
The test increases in diameter, thanks to the foliaceous folds which 
separate the segments of the wall ; the folds of two adjacent segments 
work into each other ; they are fixed at their inner edge, free at their 
outer, and secrete both laterally and externally. The whole of the wall 
is traversed by canals. 
The terga and scuta have exactly the same structure as the inner 
portion of the wall ; their growth is effected by the mantle, and they 
have on their outer surface respiratory seffe and a cellular epithelium. 
* Comptes Rendus, cxvi. (1893) pp. 405-8. 
