. Elements of Comparative Anatomy. ALTMENTAEY CANAL OF ECHIIn^ODEEIMA. 215 r â \ I Appendages of the Alimentary Canal. § 174. The above-mentioned radial CEeca of the Astero'ida might be regarded as organs differentiated from the primitive enteron, were it not that they must be regarded differently from a phylogenetic point of view. I consider that only certain other '' interradial caeca be regarded as appen- dages of this kind; they present very various de- grees of development. In the aproctous Asterida they are absent^ or are re- duced to two (Astropec- ten), while in the others they
. Elements of Comparative Anatomy. ALTMENTAEY CANAL OF ECHIIn^ODEEIMA. 215 r â \ I Appendages of the Alimentary Canal. § 174. The above-mentioned radial CEeca of the Astero'ida might be regarded as organs differentiated from the primitive enteron, were it not that they must be regarded differently from a phylogenetic point of view. I consider that only certain other '' interradial caeca be regarded as appen- dages of this kind; they present very various de- grees of development. In the aproctous Asterida they are absent^ or are re- duced to two (Astropec- ten), while in the others they are often very greatly developed. Archaster has five such CEecal sacs,divided at their ends^ and in Oul- cita this division is carried still further, so that each branch forms a racemose tube. In this way these appendages acquire the form of glands, and ex- hibit relationship with a structure which is very common in the Holothu- roida. The structure in ques- tion is connected with the terminal portion of the ahmentary canal, known as the '' cloaca," and as a rule consists of two chief trunks, with short branches, which extend. Fig. 109. Enteric canal and tree-like organs of aHolothurian. o Moiitli. i Enteric tube, d Cloaca. a Anus. c Branched stone-canal. ^ Polian vesicle, rr Tree-like organs, r' Connec- tion between them, at the opening into the cloaca, m Longitudinal muscular layer of the body. forwards throughout the whole length of the body-cavity (Fig. 109, r), and are provided with a large number of ramified cascal tubes. Although the function of these organs, which were formerly knowxi as " lungs,'^ and considered to be internal respiratory organs, is different from that of the interradial csecal tubes of the enteron of the Asterida, yet they are exactly the same morphologically, and are a further development of the simpler tubes of the Please note that these images are extracted from scanned page images that may have been digitally enhanced for
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