432 



THE IXSECTA. 



*§> 340. 



The Blood of tlie Insecta is usually a colorless liquid, though sometimes 

 yellowish, but rarely red.® In this liquid are suspended a few very small ^ 

 oval, or spheroidal corpuscles, which are always colorless, have a granular 

 aspect, and are sometimes nucleated.® 



The Dorsal Vessel, which is constricted at regular intervals, is always 

 situated on the median line of the abdomen, being attached to the dorsal 

 "wall of its segments by several triangular muscles whose apices point out- 

 "wards. Its walls contain both longitudinal and transverse fibres, and, 

 externally, are covered by a thin peritoneal tunic. Internally, it is lined 

 by another very fine membrane, which, at the points of these constrictions, 

 forms valvular folds, so that the organ is divided into as many chambers as 

 there are constrictions. Each of these chambers has, at the anterior 

 extremity on each side, a valvular orifice which can be inwardly closed.''" 

 The returning blood is accumulated about the heart and enters into it 

 during the diastole of each of its chambers, through the lateral ""orifices.'^^ 

 It then passes, by the regularly successive contractions of the heart, from 

 behind forwards into the aorta which is only a prolongation of the anterior 

 chamber. This aorta consists of a simple, small vessel, situated on the 

 dorsal surface of the thorax, and extending even to the cephalic ganglion, 

 "where it either ends in an open extremity, or divides into several short 

 branches which terminate in a like manner. ""' The length of the dorsal 

 vessel depends, in all the three states of insects, upon that of the abdomen. 

 The number of its chambers is very variable, but is, most usually, eight. <'^' 



The blood, after leaving the aorta, traverses the body in currents which 



2 The blood is red in many larvae of Chtrono- 

 ■mus. 



3 For the blood of Insecta, see fVasner, Zur ver- 

 gleich. Physiol, d. Blutes, Hft. 1, p. 26, Hft. 2, p. 

 Si., and Isis, 1S32, p. 323 ; Horn, Das Leben d. 

 Blutes, p. 9, Taf. I. and Newport, Institut. 1845, 

 p. 241, or Ann. d. Sc. Nat. III. 1845, p. 364, or 

 Froriep^s neue Notiz. XXXIV. p. 9. 



i For the structure of the dorsal vessel, see 

 Straus, Consid. &c. p. 356, PI. VIII. {Melolon- 

 tlia vulgaris) ; fVagner, Isis, 1832, loo. cit. Taf. 

 II. (larvae of Diptera and Ephemeridae), and in 

 Mailer's Arch. 1835, p. 311, Taf. V. (larva of 

 Corethra plumicornis) ; Newport, Philos. Trans. 

 1843, p. 272, and Cyclop, loc. cit. p. 976, fig. 433, 

 A. and 434 (Lucanus cervus and Asilus crabri- 

 formis) ; finally Verloren, M6m. loc. cit. p. 31, 

 PI. III.-VII. (Chironornus, Sphinx, Rhyncho- 

 plioras, Pompilus, Syrpkus, and Fespa). The 



constrictions of the dorsal vessel are feebly marked 

 with the larvae of the Diptera and Hymenoptera.* 



5 According to Newport (Cyclop, loc. cit. p. 

 977), the space in which the blood accumulates 

 about the heart is surrounded by a very thin mem- 

 brane, and may therefore be regarded as a true 

 auricle. 



6 The Aorta is divided at its extremity witfi 

 Meloe, Blaps, Timarcha, Vanessa, and Sphinx f 

 see Newport, Cyclop, loc. cit. p. 978. 



' With the Orthoptera, Lepidoptera, and their 

 larvae, as also with various larvae of Diptera. It 

 is rare that the number of cliambers exceeds eight,, 

 as, for example, with the Poduridae (Nicolet, loc. 

 cit. p. 50, PI. IV. fig. 3). More commonly there 

 are seven, as with Lucanus and Dytisciis (New- 

 port, Cyclop, loc. cit. fig. 433, A., and Wagnery 

 Icon. Zoot. Taf. XXIII. fig. 2). Burmeister 

 (Ilandb. I. p. 165) has observed only four with the 

 larva of a Calosoma. 



■worms fed on different artificially-colored leaves 

 I)roduced correspondingly colored cocoons. He 

 therefore fed, in the same manner, various larvae, 

 and, upon disssction, found not only their blood but 

 also their tracheae colored like the color used. 

 With the tracheae, this color was deepest at the 

 base, but gradually paled away towards their ex- 

 tremity. What adds a corroborating value to these 

 experiments is the fact that the muscles here re- 

 mained uncolored, tlius showing that this special 

 trachean coloration was not due to a bathing of the 

 general fluids of the body. Compare also the re- 

 cent various notes and papers of Blanchard, in 

 Ann. d. Sc. Nat. — Kd. 



* [ 5 340, note 4.) See also, for histological de- 



tails upon the heart, Le.ydig, Siebold and Köl- 

 iilcer's Zeitsch. 1852, III. p. 446 (larva of Co- 

 rethra plumicornis). This naturalist has here 

 described a new and peculiar kind of valves, which 

 deserve particular notice. In the last chamber of 

 the heart, there are six or eight pairs of roundisli, 

 clear bodies, attached to the inner surface of the 

 heart by a peduncle. They alternate in their posi- 

 tion, one beyond the other, so that, during the sys- 

 tole, two of them are so opposed that the calibre of 

 the chamber is completely closed at that point. 

 Each of these curious valves is only a pedunculated 

 nucleated cell • see loc. cit. Taf. XVI. fig. 2, c — 

 Kd. 



