656 CIRCULATION OF THE BLOOD AND DORSAL VESSEL 
vessel frequently recommence. I attribute this to the removal 
of the inhibitory influence of the ganglion cells attached to the 
pericardial septum. 
The blood which enters the pericardial septum passes over 
the great air-sacs of the thorax and abdomen, and from this 
fact, and the large number of fine trachez on the septum, there 
can be little doubt it is charged with oxygen. The dorsal 
vessel is, therefore, a true arterial heart, like that of the 
Crustacea, which sends arterial, 7.e., oxidized blood to the 
head. 
4, THE DEVELOPMENT OF THE DORSAL VESSEL. 
The manner in which the dorsal vessel is developed in the 
embryo Insect is insufficiently known. Weismann says [2, p. 85], 
describing the development of the embryo of the Blow-fly : 
‘From the position of the dorsal vessel in the larva, it is 
possible to conclude that it is developed from the deepest of 
the superticial cell layers of the embryo. During embryonic life 
I have not been able to observe it, although it is beautifully 
seen in the posterior part of the body of the young larva, in 
which it contracts 56 times in a minute.’ 
Biitschli [126] states that in the Bee embryo it is developed 
from two cell strings, which form the edges of the somatopleure 
from the neck to the posterior extremity of the larva; but he 
gives no details, and does not indicate whether there are 
several rows of cells, or only one row on each side. Jawo- 
rowski [815] admits that he was unsuccessful in tracing the 
development of the dorsal vessel in the embryo of Chironomus, 
and I have been equally unsuccessful in the Blow-fly embryo. 
Bibliography : 
314. DARESTE, C., ‘Note sur le Développement du Vaisseau dorsal chez 
les Insectes.’? Archiv. d. Zool. experimental, tom. ii., 1873. 
315. JAworowskI, A., ‘Ueber die Entwickelung des Riickengefiisses und 
speciell der Musculature bei Chironomus und einigen anderen 
Insecten.” Sitzb. der k, Acad. der Wissensch, Wien., 8vo, Bd. Ixxx., 
1879. 
