INSECTS. 259 



the air-tubes, in regular streams backwards. These 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 larvae 

 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- 

 PORT and BOWERBANK believe, or in free spaces between the 

 organs, without special walls. The writers who maintain the 

 .atter 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 1 . NEW- 

 PORT found this vessel in the genus Sphinx, and thinks that the 

 blood flows in it backAvards, 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 2 . 



The Respiratory organs of Insects are their air-canals (trachea) , 



1 Zeitsckr.fiir Pkysiol. iv. 2, 1832, s. 181 184, Taf. Xiv. fig. 13. 



3 Comp. on the dorsal vessel and the circulation of insects LYONET, Trait'e Anat. de 

 la Chenille, pp. 413, &c.; on the fluid contained in it, ibid. pp. 426, 427; HEROLD, 

 Pkysiol. Untersuchungen iiber das Rudcengefass der Insecten, Marburg, 1823, 8vo. ; 

 STRAUS Anat. comp. des Anim. articuUs, pp. 345 358 ; J. MUELLER, Nov. Act. Acad. 

 Cces. Leop. Car. Tom. xn. 2, 1825 (on a connexion between the dorsal vessel and the 

 ovaries) ; C. G. CARUS, Entdeckung eines einfachen vom Herzen aus beschleunigten 

 UlutJcreislaufes in den Larren netzfluglicher Insecten. Mit 3 Kupfert. Leipzig, 1827, 

 4to ; WAGNER, Beobachtungen ilb. d. Kreislauf des Blutes u. d. Ban des Rilckengef asses 

 bei den Insecten, OKEN'S Isis, 1832, s. 320 331, Taf. n. ; NEWPORT, TODD'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 



172 



