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Read Ebook: An Introduction to Entomology: Vol. 4 or Elements of the Natural History of the Insects by Kirby William Spence William
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Ebook has 622 lines and 167761 words, and 13 pages
CIRCULATION.
I shall now enlarge a little upon each of these hypotheses, beginning with the first or original one.
When the animal is vigorous, the current is uninterrupted, although its velocity is accelerated at regular intervals; and that not only in the excurrent , but also in the recurrent part of its course through the lamina. When the animal becomes exhausted, or the laminae exsiccated, the circulation is interrupted, and in the same manner, as under the same circumstances, in the larvae of frogs and lizards; the disturbance displaying itself not merely by a cessation of the process, but also by retrograde movements of the currents, or by oscillatory motions of the blood-globules.
In proportion as the wings are developed, the circulation in the laminae diminishes, and ultimately ceases, preparatory to the detachment of the laminae themselves. At the same time, however, it presents itself under a new form in the wings. In these the excurrent or arterial stream takes its course along the inner margin of the wing, and the recurrent or venous returning along the outer; whilst, occasionally, other transverse currents take their course through the net-work of the wing from its inner to its outer margin. As the wings are further developed, the circulation in them, like that in the caudal laminae, gradually becomes weaker and ultimately ceases.
The endeavours of M. Carus to discover any proofs of a circulation in insects in their last state, except in the wings at their first development, were without success. He observes that the fact of the currents of fluids in larvae not being defined by vascular parietes, enables us to comprehend the rapidity and facility with which the traces of the circulation are lost in the perfect insect. On the other hand, that the existence of a circulation at one period, and its cessation at another, elucidate many circumstances connected with the physiology of these animals: for instance, the contrast between the rapid growth and transformations of the larvae, and the stationary existence of the imago, &c. Lastly he remarks, that the phenomena of this circulation do not throw any light on the obscure subject of the mode of nutrition in perfect insects; which therefore must still be supposed to be effected according to the idea of Cuvier, without the intervention of vessels.
I am, &c.
FOOTNOTES:
Reaum. i. 160--.
Lyonet says , "au-del? de trois millions de fois plus petits qu'un grain de sable"!!
His words are--"In silkworms I have clearly seen various small vessels spring from and approaching to the heart, which I have even filled with a coloured liquid. But whether they were veins or arteries I cannot yet affirm." i. 112. a. 176. a. According to Cuvier , but I cannot find the passage, Swammerdam also mentions having seen a red fluid issue from small vessels in grasshoppers.
Reaum. v. 103.
Bonnet ii. 309. Perhaps in both cases the alimentary canal was the organ seen.
Reaum. iv. 171--.
Lesser L. ii. 84. note.
De Geer ii. 505--. vi. 287.
See above, p. 85.
Reaumur iv. 264.
Ibid. 260--.
Dr. Kidd did not find the abdominal viscera of the mole-cricket thus circumstanced, nor more lubricated than the intestines of the higher animals.
LETTER XL.
DIGESTION.
In the natural families of these creatures, the same analogy takes place with respect to this part that is observable in the rest of the Animal Kingdom; the length and complication of the intestines are here, as in the other Classes, often an index of a less substantial kind of nutriment; while their shortness and slenderness indicate that the insect lives by prey.
Having given you this general account of the intestinal canal and its parts and appendages, I shall now state some of the peculiarities that in this respect distinguish particular tribes and families.
I am, &c.
FOOTNOTES:
Herold says that Ramdohr is mistaken here, and denies the existence of this juice in insects; but as Ramdohr's researches were so widely extended, he is most likely to be right.
Ramdohr 103.
Ibid. FIG. 8.
Ibid. FIG. 9.
See above, p. 99--.
Treviranus and Ramdohr are of the former opinion; and Meckel, Cuvier, Marcel de Serres, and Leon du Four, of the latter.
De Geer iii. 26.
SECRETION.
Huber says that he has ascertained by a great number of observations that electricity is singularly favourable to the secretion of the substance of which honey is formed by flowers; the bees never collect it in greater abundance, nor is the formation of wax ever more active, than when the wind is in the south, the air humid and warm, and a storm gathering.
I have before mentioned the coloured fluid which some insects emit when they are disclosed from the pupa, and that it probably exhales some powerful odour which attracts the males.
I am, &c.
FOOTNOTES:
De Geer iii. 41.
De Geer iii. 111.
Reaum. v. 24.
Reaum. vi. Pref. xxviii. 177--.
Reaum. iii. 230.
Reaum. iii. 215. Bonnet ix. 182.
De Geer, v. 6.
Reaum. v. 448.
Reaum. v. 354.
A Brazilian wood so called, but differing from the common cedar.
Reaum. iii. 494.
Dated Tripoli in the West, January 21, 1819.
See above, p. 90. note^a.
See above, p. 78.
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