. The cyclopædia of anatomy and physiology. Anatomy; Physiology; Zoology. 206 ARACIINIDA. have an apparatus for circulation pretty well developed. It consists of an elongated vessel placed immediately beneath the integument along the middle line of the dorsal aspect of the back, on which account it has received the name of dorsal vessel (Jig- 89). It is kept in its situation by small ligaments or muscles, (a a), which in insects are called ales cordis. The texture of the dorsal vessel is membranous, and pretty firm; it contains a colourless fluid. This heart is in communication with numerous v
. The cyclopædia of anatomy and physiology. Anatomy; Physiology; Zoology. 206 ARACIINIDA. have an apparatus for circulation pretty well developed. It consists of an elongated vessel placed immediately beneath the integument along the middle line of the dorsal aspect of the back, on which account it has received the name of dorsal vessel (Jig- 89). It is kept in its situation by small ligaments or muscles, (a a), which in insects are called ales cordis. The texture of the dorsal vessel is membranous, and pretty firm; it contains a colourless fluid. This heart is in communication with numerous vessels, but hitherto it has not been discovered which of these terminate in, or which arise from the organ, or, in other words, it is not known by what route the blood arrives at, or proceeds from the heart. We believe that we are able to dissipate the doubts which still exist as to this subject, but before we state our opinions we shall speak of the anatomical disposition of the apparatus. Treviranus has described it vaguely in the scorpions, but has well elucidated its structure in the spiders (aranete), more par- ticularly in Clubione atrox and Tegenaria do- mestica, Fig. 89. In both these species nu- merous vessels are observed to arise from the heart, es- pecially from its posterior part (c c.) These proceed to a ramify indefinitely, distributing them- e selves over every organ; and we have no doubt e with respect to d their true arterial nature. But in ad- a dition to these ves- sels there exist two a others of larger ffl size (d d,~) which communicate in a one direction with a the heart, in an- other, by very fine ramifications, with the pulmonary branchiae. In Clu- bione atrox these two vessels do not give out any No doubt remains these vessels maintain a between the heart and The subjoined figure. Tegenaria domestica, branches in their course in our mind but that direct communication respiratory organs (jig. 89) will facilitate the understanding of these facts. It rep
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