INSECTA. 



979 



Fig. 433. 



A, dorsal vessel or heart of Lucamis cerrus. 



a, the valves or chambers ; b, b, the lateral mus- 

 cles ; c, the supposed auricular space around the 

 vessel. 



B, the dirision into vessels of the anterior or aortal 

 portion of the dursal vessel in the larva of Vanessa \irt\cae. 



C, interior of the dorsal vessel (Straus}. 



a, interior of the valve, showing the transverse 

 fibres; 6, the auriculo -ventricular opening and 

 valve into the chambers of the vessel ; c, semi- 

 lunar valve ; d, inter-ventricular valve. 



internal one (C, a) formed of a transversely 

 folded and striated membrane which is thickest 

 towards the middle of each chamber, and an 

 external one formed of strong, smooth, mus- 

 cular, longitudinal fibres. Burmeister* has 

 suggested that these may be only two layers of 

 one muscular structure, and that the presence 

 of a structureless lining or inner membrane 

 must then be presumed, although it be too 

 delicate to be actually detected by observation. 

 The third or external coat is a transparent struc- 

 tureless membrane which covers the outer 



VOL. ii. 



* Op. cit. p. 156. 



surface of the heart, and is extended du t ^ e 

 over it without following the reflexions inwai - v 

 of the muscular coat, where it forms the valves, 

 or separations between the different chambers. 

 The division of the organ into separate cham- 

 bers is effected by means of an intussusception 

 or reflexion inwards and forwards of the whole 

 muscular structures. A portion of each side 

 of the heart is first extended inwards so as 

 very nearly to meet a corresponding portion 

 from the opposite side, and then reflected back- 

 wards forms, according to Straus,* the inter- 

 ventricular valve (d), which separates each 

 chamber from that which follows it. Posteriorly 

 to this valve, at the anterior part of each cham- 

 ber, is a transverse opening or slit (6), the 

 auricula-ventricular orifice, through which the 

 blood passes into each chamber, and imme- 

 diately behind it is a second but much smaller 

 semilunar valve (c), which, like the first, is 

 directed forwards into the chamber. It is 

 between these two valves on each side that the 

 blood passes into the heart and is prevented 

 from returning by the closing of the semilunar 

 valve. When the blood is passing into the 

 chamber the inter-ventricular valve is thrown 

 back against the side of the cavity, but is 

 closed, when, by the contraction of the trans- 

 verse fibres, the diameter of each chamber is 

 narrowed and the blood is forced along into the 

 next chamber. The number of these openings 

 and chambers in different species of insects 

 does not yet appear to have been satisfactorily 

 ascertained. Straus has figured nine chambers 

 in Melolontha, and consequently eight pairs of 

 openings, but we have not been able to observe 

 more than seven pairs of openings in Lucanus 

 cervus, in which the anterior pair is almost 

 hidden at the commencement of the aorta. 

 Burmeisterf states that he could not find more 

 than four pairs of openings in the larva of 

 Calosoma, while he remarks that according to 

 Muller's description of the heart in Phasma 

 there appears to be but one pair in that species. 

 In Bombus terrestris we have as yet detected 

 but five pairs, but we nevertheless suspect that 

 these discrepancies, or apparent differences in 

 the number of these openings, arise less from 

 so great a diversity in the actual number than 

 from some of them being overlooked during 

 dissection, since we have invariably found eight 

 pairs in Sphinx ligustri, both in the larva and 

 perfect state, as well as in other Lepidoptera; 

 while in the Bombus examined by us the 

 dissection was not so carefully made as to 

 enable us to state positively that there are not 

 more than we have mentioned. The external 

 form of the chambers in the very thick and 

 muscular heart of Lucanus is shown in the 

 drawing we have given of this structure. When 

 the heart is examined by transmitted light, there 

 is seen around it a bright space (A, c) in which 

 we have observed the blood flowing very freely 

 in living specimens afj&grum, and which we 

 regard with Straus as an auricular cavity, 

 apparently bounded by a loose membrane, and 



* Considerat. &c. p. 356. 

 t Op. cit. p. 154. 



3 S 



