Elementary text-book of zoology, general part and special part: protozoa to insecta . elementarytextbo00clau Year: 1892 280 ECHI>*ODEBM±TA. or lesa pear-shaped larva, in whicli a slightly arched dorsal, t'wo symmetrical lateral, and a saddle-shaped ventral surface can be dis- tinguished. The cilia which are concentrated upon the raised edge of the ventral depression give rise to a continuous ciliated band which serves as a locomotive apparatus. [This band first appears as two f-eparate ciliated ridges placed ^ely, one in front of, and the other behind the mouth (fig. 224, 3). The
Elementary text-book of zoology, general part and special part: protozoa to insecta . elementarytextbo00clau Year: 1892 280 ECHI>*ODEBM±TA. or lesa pear-shaped larva, in whicli a slightly arched dorsal, t'wo symmetrical lateral, and a saddle-shaped ventral surface can be dis- tinguished. The cilia which are concentrated upon the raised edge of the ventral depression give rise to a continuous ciliated band which serves as a locomotive apparatus. [This band first appears as two f-eparate ciliated ridges placed ^ely, one in front of, and the other behind the mouth (fig. 224, 3). These soon become con- nected laterally.] The alimentary canal, which has now acquired an anterior opening, the mouth, consists of three portions,—the oeso- phagus, the stomach, and the intestine. The wide mouth leading into the oesophagus is situated within the band of cilia on the ventral surface; the anus is also ventral, but external to the ciliated band in the region of the posterior pole. Before the appearance Pia. 221.—Larval development of Atteracanthion heiylintig (after A. Agassiz) (for earlier stages see fig. 103). 1, stage where the mouth (O) has just appeared, represented in profile; ^.blastopore (anus); 2>, intestine; 1'p, vaso-peritoneal sac. 2, Somewhat older stage in surface view with two separated vaso-peritoneal sacs. 3, Later stage, from the ventral side, with two transverse ciliated ridges (W); the sac on the left side has an excretory pore. 4, Young Bipinnaria with double band of cilia (IVJ. of the mouth, another organ is separated horn, the alimentary canal: this is a sac-like ciliated tube, which opens to the exterior by a pore on the dorsal surface, and represents the first commencement of the ambulacral system, A second organ, which also has its origin from the rudimentary digestive canal, consists of the disc-shaped lateral sacs (fig. 224), from the walls of which the peritoneal lining of the body cavity is produced. With their progressive dev
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