The above-named substances comprise those which in the vertebrates effect a change in the activity of the motor nerve-ganglia of the heart and the muscular fibres. Hence it follows that the heart of the larval Corethra consists of muscular fibres provided with ganglia, and that the contractions of the muscular fibres are provoked through the agency of the ganglia. But since muscarine, atropine, and curare, whose influence in stopping the heart’s action of vertebrates is known, in insects either have no action or only make the pulsations slower; it seems to follow that the heart of the larval Corethra possesses no similar apparatus for lessening the heart’s action, and this is also confirmed by anatomical studies. On the contrary, aconite acts, as we must from observations conclude, exclusively on the motor centres and the muscles, but not on the apparatus for lessening the heart’s action, which, as has been remarked, is not present in the larval Corethra. (Kolbe ex Dogiel.)
Dewitz has discovered an onward movement of the blood corpuscles, somewhat independent of the general circulation. This independent motion of the blood corpuscles is not only a creeping one like the amœboid motion of the white corpuscles of vertebrates, but they have besides a peculiar swimming movement. Dewitz noticed this in the hind wings of a recently emerged meal-worm beetle (Tenebrio molitor), still white and soft, after they had been cut off. The tissues forming the matrix within the wings constitute a network filled with blood. The current of blood within the wing thus cut off may be stopped flowing by a tap on the firmly clamped object-bearer on which the wing is placed, or by drawing it by an apparatus described by the same author, to incite in one way or another the blood corpuscles to swim forwards. When a corpuscle is disposed to move, we see it first stirring restlessly, or wabbling about, in this way changing its form; then it moves forwards, and does not come to a standstill. If it remains still there, after a while, by tapping, it begins again its movements.
“Should one yet doubt the fact of this spontaneous movement of the blood corpuscles, he will surely be convinced of its correctness by observing the so-to-speak reluctantly springing motion of a blood corpuscle in the wing of Tenebrio molitor with the simultaneous change of appearance and shape of the corpuscle.”
This spontaneous or independent motion of the blood corpuscles is also produced by the heating apparatus. As soon as the corpuscles lie still in the severed wing and they are warmed, the corpuscles begin to pass through the meshes of the tissue. When cooled, the motion ceases, but as soon as the temperature rises to a certain grade, the corpuscles again move onwards.
To explain this independent motion Dewitz thinks that they take up and then expel the blood-fluid, and in this way cause their motion. This independent motion is necessitated, in order that the stream of blood may become so regulated, that the blood corpuscles shall not be arrested in their course, but even turn back again out of the farther end of the antennæ and limbs. The chief mechanical power for the blood circulation must go on independently of the propulsatorial apparatus and of the heart. (Kolbe.)
LITERATURE ON THE HEART AND ON THE CIRCULATION OF THE BLOOD
a. Anatomy of the organs
Meckel, J. F. Ueber das Rückengefäss der Insekten. (Meckel’s Archiv, i, 1815, pp. 469–476.)
Müller, J. G. De vasi dorsali Insectorum. Berolini, 1816, pp. 22.
Serres, P. Marcel de. Observations sur les usages du vaisseau dorsal ou sur l’influence que le cœur exerce dans l’organisation des animaux articulés, etc. (Ann. du Mus. d’hist. nat., 1818, iv, pp. 149–192, 313–380, 2 Pls.; v, 1819, pp. 59–147, 1 Pl.)