‘INSECTS. 259 
the air-tubes, in regular streams backwards. ‘hese streams of 
blood on the outside of the heart were first observed by Carus 
twenty years ago in the three fin-shaped caudal processes of the 
larva of Agrion ; afterwards he observed a similar motion of fluid 
in the imperfect wings of the Nymphs; the blood-globules (accord- 
ing to many, rather according to VERLOREN, the fat-globules), which 
swimming in a clear fluid indicate the direction of the current. 
The later observations of various authors, on transparent larvee 
principally, have ascertained the phenomenon in Insects of every 
order—and it may therefore be confidently accepted as general. A 
question which requires further investigation for its solution is 
this, whether the circulation is effected in vessels, as ex. gr. NEW- 
PporT and BoweErRBANK believe, or in free spaces between the 
organs, without special walls. The writers who maintain the 
latter opinion, allege that the Aorta has an open termination in 
the Head. In the Myriapoda, besides the dorsal vessel, there are 
still others present; amongst which a trunk that lies upon the 
nervous cord in the abdomen, ought to be mentioned. In the 
Butterflies also. TREVERANUS discovered on the ventral surface a 
vessel, lying on the nervous cord and running longitudinally, from 
which on each side numerous transverse branches arise}. NEW- 
Port found this vessel in the genus Sphinx, and thinks that the 
blood flows in it backwards, as it does forwards in the aorta. This 
last author discovered in this same genus, and in certain Coleoptera 
branches from the aorta in the head, but was not able, on account 
of the delicacy of the ‘parts, to follow their further course?. 
The Respiratory organs of Insects are their air-canals (trachee), 
1 Zeitschr. fiir Physiol. tv. 2, 1832, s. 181—184, Taf. xIv. fig. 13. 
2 Comp. on the dorsal vessel and the circulation of insects Lyonet, Traité Anat. de 
la Chenille, pp. 413, &c.; on the fluid contained in it, ibid. pp. 426, 427; HeRoxp, 
Physiol. Untersuchungen tiber das Riickengeftss der Insecten, Marburg, 1823, S8vo. ; 
Straus Anat. comp. des Anim. articulés, pp. 345—358 ; J. Munturr, Nov. Act. Acad. 
Ces. Leop. Car. Tom. XII. 2, 1825 (on a connexion between the dorsal vessel and the 
ovaries); C. G. Carus, Entdeckung eines einfachen vom Herzen aus beschleunigten 
Blutkreislaufes in den Larven netzfliiglicher Insecten. Mit 3 Kupfert. Leipzig, 1827, 
4to; WaGNeER, Beobachtungen ib. d. Kreislauf des Blutes u. d. Bau des Riickengefésses 
bet den Insecten, OKEN’S Isis, 1832, s. 320—331, Taf. 11.; Newport, Topp’s Encyclop. 
II. pp. 975—982. The treatise of our excellent M. C. VERLOREN, crowned by the 
Brussels Academy of Sciences in 1844 (!) is impatiently waited for ; I have made use 
of the observations he had the goodness to communicate to me when treating of the 
dorsal vessel. 
17—2 
