Elements of comparative anatomy (1878) Elements of comparative anatomy elementsofcompar00gege Year: 1878 112 COMPAEATIVE ANATOMY. gastric pores), which have consequently a dermal and gastric orifice, is generally very great; their number is dependent on that of the spaces which are bounded by the rays of the spicula (cf. Fig. 36, o). These characters are very distinct in the lowest forms of the Calci- spongia?, the Ascones (Olynthus). The development of diverticula of the enteric cavity gives rise to a second form; the diverticula are continued into the correspondingly thickened ectoderm, whe
Elements of comparative anatomy (1878) Elements of comparative anatomy elementsofcompar00gege Year: 1878 112 COMPAEATIVE ANATOMY. gastric pores), which have consequently a dermal and gastric orifice, is generally very great; their number is dependent on that of the spaces which are bounded by the rays of the spicula (cf. Fig. 36, o). These characters are very distinct in the lowest forms of the Calci- spongia?, the Ascones (Olynthus). The development of diverticula of the enteric cavity gives rise to a second form; the diverticula are continued into the correspondingly thickened ectoderm, where they form more or less branched canals ; from these, again, fine canals, which are also branched, open into the dermal pores. The enteric cavity, as it becomes more and more divided into branched canals, loses its importance as a stomach, and at the same time its endodermal investment, which is now limited to the branched canals. But the endodermal layer does not extend over all of them, but is finally restricted to their diverticula, which are thus converted into the so-called ciliated chambers. Thus the function of the enteric tube passes more and more from its primitive locality into the addi- tional spaces, which are gradually developed from it. The subjoined figure (Fig. 42) represents the last stage in which the endoderm invests the ciliated chambers only (w). Modifications of this form which obtains in the group of the Leu- cones, among the Cal- cispongia3, are formed by the union of the branched canals and of the ciliated chambers one with another, whence arise retiform canal systems. The Siliceous and fibrous Sponges conform to this type. A third form arises by the formation of closely adjoining canals, directed radially to the stomachal cavity, which in their characters correspond to the simple Ascon form, but which generally communicate with the exterior Fig. 42. Diagram of the gastric system of a Leucou (Dyssycus ananas), where branched canals are developed, o
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