180 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
Follicle Cells in Molgula.* — M. Antoine Pizon returns to the old 
problem of the follicle cells and cellules de rebut in Tunicates, having 
studied the case of Molgula socialis. Ovarian follicle cells accompany 
the ovum, and multiply by mitosis to form a primitive follicle. This 
becomes differentiated into an external and an internal follicle, and the 
latter more or less degenerates. Quite distinct therefrom are the cellules 
de rebut , which appear endogenously within the ovum, are expelled, and 
form a layer within the internal follicle. 
INVERTEBRATA. 
Nerve-Cells of Invertebrates.! — Herr M. Pfliicke has studied the 
fine structure of the nerve-cells in earthworm, crayfish, snail, cuttlefish, 
&c. His general conclusions are the following : — (1) The cell-substance 
consists of varicose fibrils, which form a network around the nucleus ; 
in Lumbricus the anastomoses occur at the origin of the processes. The 
varicosities are peculiar to the plasmic fibrils, being apparently absent 
from those of the axis-cylinder. 
(2 ) The nuclear framework of the nerve-cell consists of a system of 
uniformly thick threads, which radiate out from the nucleolus and branch 
in a reticulate fashion within the nucleus. The terminal strands pass 
into the nuclear membrane. The threads of the framework bear the 
granular chromatin. 
(3) The nuclear membrane has knot-like thickenings, like those of 
the plasma-fibrils. These knots form the junctions of the terminal 
threads from the plasma and from the nuclear framework. 
Thus the nuclear membrane is not a cuticular product, but a fusion 
of nuclear and plasmic constituents. 
Mollusca. 
y. Gastropoda. 
Air-breathing “ Prosobranchs ” and Gill-bearing “Pulmonates.” } 
Hr. Paul Pelseneer criticises the terms Prosobranch and Pulmonate, and 
gives several new examples of variation in the respiratory organs in 
these Molluscs in accordance with the habitat. In the “ Prosobranchs, ” 
adaptation to an aerial life may take place in three ways. First by a 
modification of the etenidium, second by the formation of a lung which 
is equivalent to the whole paliial cavity, and third by the formation of a 
lung equivalent to the left part of the paliial cavity. The first modifica- 
tion occurs for example in Littorina , Cremnoconchus, and Neritina; the 
second in Cerithidea obtusa and many others; and the third in Ampul- 
laria. In all there is not merely modification of the etenidium, but also 
of the circulatory system, while the hypobranchial gland and the os- 
ph radium tend to disappear, the former being replaced by a vascular 
network. 
Similarly, the Pulmonata may be adapted to aquatic life in the 
following ways: — By the association of a secondary branchia with an 
aquatic lung ( Planurbis naulileus ) ; by the association of a secondary 
* Comptes Rendus, exxii. (1896) pp. 40-2. 
f Zeitschr. f. wiss. Zool., lx. (1895) pp. 500-42 (1 pi.). 
X Arch. Biol., xiv. (1895) pp. 351-93 (2 pis.). 
