-S14.] On the Uses of the Dorsal Vessel. 353 



with ink and coloured liquids. He concludes from tin's absence of 

 blood-vessels, and from the communication which exists by means 

 of fibrilliB between all the internal parts of insects, and from the 

 fatty bodies spread every where, that these bodies draw their nourish- 

 ment from the fat by means of the fibrillar. Hence other uses of 

 the dorsal vessel must be sought for, and the one pointed out by 

 Lyonnet does not appear to be the least essential, as the facts which 

 we shall state in this memoir will show. 



Comporetti, to whom we owe a great number of anatomical 

 observations, and who had the glory of labouring with Scarpa i ri a 

 very difficult undertaking, is the only person who has admitted 

 without any restriction a double vascular system in insects properly 

 so called. This double system extends, according to him, to all 

 the membranes and all the viscera. It is particularly related to the 

 muscular system.* .By this admission of a double system, Compa- 

 retti was forced to conclude that the liquid contained in the dorsal 

 vessel has a circulation, and that it flows upwards, as in the common 

 earth-worm. f He thinks likewise that the contractions and dilata- 

 tions of the dorsal vessel are not equal, and that they are more or 

 less considerable, according as they are examined in different parts. 



Passing then to the examination of the vascular vessels, he 

 describes them in the fly, observing that the lateral trunks which 

 have movements of contraction terminate in two white and oval 

 bodies. Two vascular trunks give, according to him, large branches, 

 diverging on the internal surface of the ring as on the heart and 

 oesophagus. He says likewise that he perceived radiated filaments 

 on the surface of the two muscles at the side of the ring, and there 

 to have reckoned 150 pulsations in a minute. As to the movement 

 of contraction and dilatation, it appeared to him to commence at 

 the base, and to continue several hours after he had made a lateral 

 section. % In the bee-formed fly, which he calls mosca apiformis, 

 he says he observed the dorsal vessel presenting lateral and vibrating 

 ramifications. These ramifications communicate with others, which 

 extend in the abdomen, and vibrate like the heart. Some of them 

 exhibit a pretty frequent pulsation, others very striking undulations. 

 I have often observed in a great number of insects, especially in the 

 scolopendras, very strong contractions of the muscular fibres, espe- 

 cially in those which go to the claws. These contractions extend 

 transversely from one side of the muscles to another, and arefso 

 distinct that we might believe them to be produced by some ramifi- 

 cations of the dorsal vessel ; but as this vessel has no ramifications, 

 these contractions must depend upon the muscles themselves. Hence 

 Comparetti might have been easily deceived by these contractions, 

 and might have believed them produced by branches of the dorsal 

 i I, especially as, in some species, the trachea; have a violet 

 colour, or a dark red with a shade of blue. Comparetti is not 

 satisfied with describing the pulsations of the ramifications of the v 



♦ Diaaroiea Ankulr, Part L p. 23C. + ll>id. p. 811. Ibid. p. 216, 



Vol. IV. N° V. Z 



