. Text-book of embryology. Embryology. 378 INVEETEBEATA CHAP. {, Fig. 306) are shed into the coelom aud are there taken up by amoebocytes and absorbed. In this way, gradually, the whole of the prototroch is disposed of. During this process the larva takes on a cylindrical form with a diminishing ring-shaped swelling in front; this swelling is the disappearing prototroch. A nerve strand runs from the cerebral ganglion to the apical sense-organ, and from this ganglion originate a pair of muscle cells. imc Fig. 306.—Nearly sagittal through metamorphosing trochophores of
. Text-book of embryology. Embryology. 378 INVEETEBEATA CHAP. {, Fig. 306) are shed into the coelom aud are there taken up by amoebocytes and absorbed. In this way, gradually, the whole of the prototroch is disposed of. During this process the larva takes on a cylindrical form with a diminishing ring-shaped swelling in front; this swelling is the disappearing prototroch. A nerve strand runs from the cerebral ganglion to the apical sense-organ, and from this ganglion originate a pair of muscle cells. imc Fig. 306.—Nearly sagittal through metamorphosing trochophores of ,. A, sagittal section to one side of the middle line of the Larva of Phascolosoma gouldii^ about fifty-seven hours old, to show the segments of the mesodermal band. (After two figures by Gerould combined.) B, sagittal section nearly median of the larva of Phas- colosoma vulgare, about forty-eight hours old. (After Gerould.) a, anus; ap, apical plate; coe, coelomic cavity ; end, eudodermic tube; mesl, rnesS, vies'i, segments of the mesodermic band ; , point of origin of tlie mesectoderra ; mtr, metatroch; n,coU, nerve collar ; 2^^-<!^ prae-oral circle of cilia ; j)ir, degenerate prototrochal cells ; accessory retractors ; retd, dorsal retractor muscles formed from ectodenn; , ventral retractor muscles formed from ectoderm ; , supra-oesopliageal ganglion ; atom, stomodaeum ; , ventral nerve cord ; , yolk- granules, remains of prototrochal cells. which run backwards and are inserted into the dorso-lateral region of the skin behind the prototroch. At the sides of the ventral nerve plate there are situated two series of clusters of muscle cells. The more ventral of these run backwards towards the posterior insertion of the retractors; the more dorsal extend forwards to the region between prototroch and post-oral circlet. The invagination of the anterior region of the body, so as to form. Please note that these images are extracted from scanne
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Keywords: ., bookcentury1900, bookdecade1910, bookpubli, booksubjectembryology
