196 KARL WILHELM GENTHE, 
has given full particulars as to the histology, I need not dwell longer on 
this subject. In some of my sections I got a nice differentiation of these 
liver cells. The sections were treated with Benpa’s Iron Haematoxyline. 
The cells of the stomach epithelium appear pale gray, while the 
liver cells alone are stained: light blue, droplets (secretion) black. 
There are present fine muscle fibres everywhere between the 
wall of the stomach and the body wall which have to be regarded 
as muscles of the body wall (Fig. 16). The violent rhythmical move- 
ments of the body must keep the stomach well shaken all the time. 
As to the other organs and their histology I have scarcely 
anything to add to the careful descriptions and drawings of BERNDT'S. 
Circulation. 
There are no special organs for circulation. The blood is red 
and the pink colour of the animal is caused by it. When injured 
the red blood flows very freely and the animal turns visibly pale 
and finally whitish. Blood lacunae are found everywhere among 
the tissues but especially in the mantle and the “ovigerous frenae” 
of Darwın, the two longitudinal folds which hang down from the 
mantle in the mantle cavity. These are the gills, but as pointed 
out by BERNDT, respiration goes certainly on not only in these but 
all over the mantle (except the disk). The mantle is thin and 
contains always much blood in its numerous lacunae. 
The contractions of the mantle and its “boring” movements as 
described by Avrivintivs and on the other hand the constant 
rhythmical protrusions and retractions of the body, undoubtedly keep 
the flow of blood a-going. Water is constantly drawn into the 
mantle cavity, churned and expelled again. Thus the great surface 
of the mantle which is still enlarged by the curtain-like flaps of the 
gills offers enough opportunity for the exchange of gases. 
A few words remain to be said about the appearance and 
behaviour of the living animal in and outside of its boring. 
The living animal as mentioned before has a pink colour. The 
muscles of the mantle are seen distinctly as darker striae. Parts of 
the stomach appear greenish through the mantle. The ovaries seen 
through the mantle are orange or brownish red and single mature 
eggs lying in the mantle cavity are whitish yellow or cream colour. 
That the pink colour is due to the red blood was mentioned above, 
it disappears as soon as the blood flows out. 
