Lz 
PSKCHE:. 305 
so that the returning stream is along the 
ventral half and in both lateral portions 
of the labium. Each of the two streams 
of blood next toward the dorsum, from 
the one which supplies the labium enters 
the outer side of a maxilla, flows along 
the outer side nearly to the distal end of 
the basal joint of the maxilla, and _ re- 
turns along the inner side of the joint 
to the head. The two streams next in 
order, as the dorsal side of the head is 
approached, are those that supply blood 
to the mandibles. Each of these streams 
enters the mandible on its inner side, 
flows nearly to its tip, and returns on 
its outer side. Dorsally from the streams 
supplying the mandibles are the streams 
that flow into the antennae, which, in 
the larvae of Hydrophilus are used as 
trophi. Each stream enters its antenna 
on the inner side, flows to the distal end 
of the basal joint, and returns on the 
outer side of that joint to the head. 
After their return to the head, the cur- 
rents of blood from the antennae and 
trophi are lost among the muscles of the 
head. 
I have attempted, in fig. 5, by arrows. 
to give a more readily comprehensible 
idea of the direction and extent of the 
above-mentioned streams of blood, than 
can be given by mere description. To 
complete the figure one should imagine 
a stream of blood toward the head, be- 
neath the arrow in the middle of the 
labium: that is, with the head in the 
position indicated in the figure, the mi- 
croscope can be focused first on a stream 
flowing outward in the labium, and then, 
with the fine adjustment, the tube of 
the microscope can be lowered until a 
return stream toward the head is brought 
into focus. I have not attempted to in- 
dicate, on the sketch, the currents of 
blood’ in the head, as they would too 
reatly complicate the figure. | 
Oo 
ton) 
Fic. 5.—Dorsal view of head of young larva of Hy- 
drophilus 2piceus, Direction of blood-currents in the 
appendages indicated by arrows. Dotted lines indicate 
partitions between blood-currents. @, antenna; #7, man- 
dible; mx, maxilla; 7, labium. Magnified 20 diameters - 
The currents of blood are not, of 
course, confined in cylindrical arteries 
and veins, as they are in the vertebrates, 
and, consequently, I have used the terms 
streams and currents of blood. These 
streams .of blood occupy nearly the 
whole interior cavity of the appendages 
in the larvae of Hydrophilus, the outward 
and return currents being separated by 
partitions, of apparently a porous nature, 
which are represented in the figure by 
dotted lines. partitions, like 
those described by C. G. Carus! in the 
abdominal appendages of the larvae of 
These 
1 Carus, C. G. Entdeckung eines einfachen vom Her- 
zen aus beschleunigten Blutkreislautes in den Larven 
netzfliiglicher Insecten. Leipzig, 1827. 
