. The Cambridge natural history. Zoology. DEVELOPMENT 435 within themselves, they develop a temporary stomach and a large sucking organ, and become for a time independent sucking animals, imbibing the fluids in the common sac, and arranged around its circumference with their mouths directed towards the centre. Svxbsequently a second embryonic stage is entered upon, the sucking organ being discarded, and the albuminous matter which the larva has imbibed being treated anew like the original yolk of the egg. It is an interesting fact that in this second embryonic stage a well-marked " tail&q
. The Cambridge natural history. Zoology. DEVELOPMENT 435 within themselves, they develop a temporary stomach and a large sucking organ, and become for a time independent sucking animals, imbibing the fluids in the common sac, and arranged around its circumference with their mouths directed towards the centre. Svxbsequently a second embryonic stage is entered upon, the sucking organ being discarded, and the albuminous matter which the larva has imbibed being treated anew like the original yolk of the egg. It is an interesting fact that in this second embryonic stage a well-marked " tail" or post-abdomen is formed, and the ganglionic nerve-masses increase in number, a cerebral mass being followed by eight pairs of ganglia in the body and eight in the A B Fig. 224.—Three stages in the deTclopment of Chelifer. A, Segmenting ovum ; B, embryo, with post-abdomen, maximum number of ganglia, and developing sucking apparatus ; C, larva. (After Barrois.) Subsequently a great concentration takes place till, besides the cerebral mass, only five closely-appHed pairs of ganglia remain, corresponding to the pedipalpi and the four pairs of legs. More- over, the first pair advances, so as to lie on the sides of, and not behind, the oesophagus. There are two ecdyses or moults during development, a partial moult, concerning only the ventral surface of the " pro-embryo " as it assumes the larval form, and a complete moult at the final stage, before emergence from the incubating sac. At the end of winter the mother cuts a hole in the silken web, and the young brood issues forth.^ ' For the embryology ofChernetidea, see J. Barrois, "Mem. sur le developpement des Ch(51ifers," Rev. Suisse de Zool. iii., 1896. Metschnikoff, Zeitsdir. wiss. Zool. xxi., 1876, p. 514 ; and Vejdovsky, Concjres zool. international de Moscou, 1892, p. 120, may also be Please note that these images are extracted from scanned page images that may have been digitall
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