. Elements of comparative anatomy. Anatomy, Comparative. 1 QO IOji Fig. 73. En- teric canal of Sanguisuga. o (Esophagus, c Posterior pair of ca^ca. a Anus. Fig. 74. Enteric canal of Aphrodite, o An- terior portion. & Middle (muscular) portion of the fore-gut. c Branched caacal appendages of The metamerism of the body in the Annulata affects the en- teric tube; but there are various other differentiations in it, which are due to adaptations to special modes of life. Here again the enteric canal begins as a csecal invagination. The aproctous condition, which persists in most of the Platyhelm
. Elements of comparative anatomy. Anatomy, Comparative. 1 QO IOji Fig. 73. En- teric canal of Sanguisuga. o (Esophagus, c Posterior pair of ca^ca. a Anus. Fig. 74. Enteric canal of Aphrodite, o An- terior portion. & Middle (muscular) portion of the fore-gut. c Branched caacal appendages of The metamerism of the body in the Annulata affects the en- teric tube; but there are various other differentiations in it, which are due to adaptations to special modes of life. Here again the enteric canal begins as a csecal invagination. The aproctous condition, which persists in most of the Platyhelminthes, is passed through by these forms at an early stage in development. The entrance to the fore-gut is most the mid-gut. a Anus. -a variously differentiated in the Hirudinea. In some the pro- tractile oesophagus is greatly complicated, in others its en- trance is armed with chitiuous ridges, which are the first signs of jaws. But in most the mid-gut is beset by pouch-like diverticula (Fig. 73), which are branched in Clepsine; the last two of these diverticula sometimes form longer caecal tubes (c) on the narrow hind-gut, which extends to the end of the body (Clepsine, Hsemopis). These are the only caeca of the gut of Aulacostomum. In others the caeca are merely indicated by constric- tions. In all cases these arrangements correspond to the metamerism expressed also in the nerve- chord. In nearly all Annelids the fore-gut is separated into several, often very different, portions. A median portion is distinguishable by its more powerful muscular investment, and is separated from the mid-gut by a tract of varying length. Among the Scoleina, this portion, which is known as the " muscular stomach," is very greatly de- veloped (Lumbricus). It forms the end of the fore-gut. It is placed more towards the middle of the latter in most Chaetopoda, and is frequently provided with denticles, which work on one another like. Fig. 75. Maxillary apparatus of a Euni- cea (Lysidico)
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Keywords: ., bookcentury1800, bookdecade1870, booksubjectanatomycomparative
