Elements of Comparative Anatomy (1878) Elements of Comparative Anatomy elementsofcompar78gege Year: 1878 ALI^ffiNTAEY CANAL OF C (ELECTEE AT A. Ill known; just as uncertain is tlaat o£ tlie two ciliated surfaces, on eitlier side of this vesicle—the polar areas, wliicli are surrounded by sliort fringe-like processes. Alimentary Canal. § 86. With the separation of the body into an ectodermal and an endodermal layer, we get the lowest condition of the organs of nutrition; the endoderm investing a space which is open to the exterior, and which is the earliest distinct digestive cavity (stomach, e
Elements of Comparative Anatomy (1878) Elements of Comparative Anatomy elementsofcompar78gege Year: 1878 ALI^ffiNTAEY CANAL OF C (ELECTEE AT A. Ill known; just as uncertain is tlaat o£ tlie two ciliated surfaces, on eitlier side of this vesicle—the polar areas, wliicli are surrounded by sliort fringe-like processes. Alimentary Canal. § 86. With the separation of the body into an ectodermal and an endodermal layer, we get the lowest condition of the organs of nutrition; the endoderm investing a space which is open to the exterior, and which is the earliest distinct digestive cavity (stomach, enteron)—(cf. supra, § 28). This condition is simplest in the Gastrula form, and undergoes various diiferentiations in the two chief divisions of the Coelenterata. The stomachal cavity, that is, does not remain a mere simple space, but grows out into various kinds of cavities, canals, pouches, and so on, which are either distributed irregularly in the organism, or are arranged in a definite way. As a rule, division of labour takes place at the same time, and only one definite part, or several such parts, functions as a digestive cavity, while the other spaces are used to distribute the nutrient fluid (chyme). But this gastric system has other functions too. There is no doubt that it also has a respiratory function, by distributing through the body the water that was taken in with the food; and for this purpose it has, especially in the Spongife, a much more extended surface than has the outside of the body. Finally, it has important relations to reproduction, for the generative elements are formed in its walls. § 87. Among the Spougiaa the simplest form is limited to the early stages of development, or is per- manent as in the Grastrgeades. Almost the only complication in the Gastrteades is the de- velopment of an arrangement for producing a current at the entrance of the simple enteric tube. In the Porifera there are various new complications. Temporary spaces appear in
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