. The Cambridge natural history. Zoology. INTERNAL ANATOMY OF CLADOCERA 43 intestine is usually straight, but in Lynceidae and in some Lyncodaphniidae it is coiled ( Peracantha, Fig. 14). In Leptodora the alimentary canal is altogether remarkaljle ; the oesophagus is a long and very narrow tube, which runs back through the whole length of the thorax and joins the mid-gut in the third abdominal segment. The mid-gut is not differentiated into stomach and intestine ; it has no diverticula of any kind, and runs straight backwards to join the short rectum a little in front of the anus. The hear
. The Cambridge natural history. Zoology. INTERNAL ANATOMY OF CLADOCERA 43 intestine is usually straight, but in Lynceidae and in some Lyncodaphniidae it is coiled ( Peracantha, Fig. 14). In Leptodora the alimentary canal is altogether remarkaljle ; the oesophagus is a long and very narrow tube, which runs back through the whole length of the thorax and joins the mid-gut in the third abdominal segment. The mid-gut is not differentiated into stomach and intestine ; it has no diverticula of any kind, and runs straight backwards to join the short rectum a little in front of the anus. The heart is always short-, and never has more than a single pair of lateral openings; it is longest in the Sididae, which show some approximation to the Phyllopods in this, as in the slight decree of difference be- tween their anterior and posterior thoracic limbs. Tlie pericardium lies in the one or two anterior thoracic segments, dorsal to the gut. From the heart the blood runs forwards to the dorsal part of the head, and passes backwards by three main channels, one entering each side of the carapace, while the third runs down the body, beneath the alimentary canal to dilate into a large sinus round the rectum. This ventral blood-channel gives a branch to each limb, which forms a ct)n- siderable dilatation in the epi])odite, the Wood from the liml) returning to the pericardium 1)y a lateral sinus. From tlu; rectum a large sinus runs forwards to the pericardium along the dorsal wall of the body. 'riic l)lo«)d which enters each half of the carapace is collected in a meiliau vessel and returned through this to the pericardium. Those spaces between the which are not filled witli blood are occupied by a peculiar connective tissue, consisting of rounded or ])olyhedral cells, charged with drops of a fatty material which is often l)rightly coloured. The reproductive organs are interesting l)ecausc of the peculiar phenomena connected with the nutrition of tin' two kinds of etrfis.
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Keywords: ., bookauthorsh, bookcentury1800, bookdecade1890, booksubjectzoology
