9. INTERNAL ANATOMY AND PHYSIOLOOY
263
it into the arteries; simultaneously, the pressure decreases in the
pericardium and blood is therefore drawn into it from the efferent
branchial channels. When the heart expands, a rise of pressure in the
FIG. 99. The flow of blood in part of a gill filament. abv, afferent branchial vein;
ebv, efferent branchial vein ; cv, connecting vessel. (After Mauchline, 1958a.)
pericardium forces the ostia open and blood flows into the heart. The
chemical characteristics of the blood of euphausiids are unknown as is
the function of the peculiar blood gland, so far described only in
M . norvegica. This gland is present in the dorsal anterior region of the
pcricardium
abdominal ~ a r t e r i e s ~ ~ ~ ~ a r t ~ e ~ e r ~ n t
thoracic
b?anchial f
sinu\
7 efferent branchial
afferent branchial
,afferent branchial
6 ’ _
e
posterior ventral
thoracic sinus
channels
veins
veins
channels
} in gills
FIG. 100. Schematic representation of the circulatory system of euphausiids. (After
Mauchline, 195%)
cephalothorax, above the cerebral ganglion and, according to Raab
(1915)) blood corpuscles are produced in it. Groups of tegumental
glands, rosette shaped with canals passing through the epidermis and
cuticle to the outside of the animal, are also present in this region.