Identifier: textbookofcompar01lang (find matches)
Title: Text-book of comparative anatomy
Year: 1898 (1890s)
Authors: Lang, Arnold, 1855-1914 Bernard, Henry Meyners Bernard, Matilda Haeckel, Ernst Heinrich Philipp August, 1834-1919
Subjects: Anatomy, Comparative
Publisher: London, New York, Macmillan and Co.
Contributing Library: MBLWHOI Library
Digitizing Sponsor: MBLWHOI Library

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n consequence ofthe fusing of pairs of ganglia which were separate in the emliryo. The whole centralnervous system arises in a manner similar to that in other Arthrt/j»><ln. 7. The Mesoderm of the Arachnoidea at a certain embryonic stage is developedjust as in the Annulata, Protrachcata, Automata, and perhaps also the Crustacea,in the form of 2 lateral segmented streaks or bands with segmental cavities. 8. The fore- and hind-guts develop in the well-known way as imaginations ofthe ectoderm (stomodaeum and proctodseum). Opinions still differ as to the mannerof formation of the tube of the mid-gut. 9. The first rudiments of the lungs (book-leaf trachere) appear as imaginations ofthe ectoderm, and thus in the same way as the tracheae in the Antennata. 10. Most Arachnoidea when born or hatched from the egg resemble the adult.As far as we know, a post-embryonic metamorphosis occurs only in the Pseudo-scorpionidce and Acarina. The former are hatched in a very imperfect condition, but
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a a PIG. 380.—A, B, C, Embryos of Agelena labyrinthica at three stages of development; in A andB supposed to be spread out flat, in C in the natural form from the ventral side ; Id, frontal lobes ; st,stomodseura ; 1-6,1st to 6th pairs of extremities (of the cephalo-thorax); viz. 1, the chelicera?; 2, thepedipalps; 3-6, legs; a, rudiments of abdominal limbs; aw in C spinning mammilla; (after Balfour). remain for some time (parasitically) attached to the body of the mother, who carriesthe eggs about with her. The young lame of the Acarina (Fig. 361, p. 514) are stilldevoid of the last pair of extremities, i.e. of the 4th pair of legs. The metamorphosisin the Acarina is often very complicated, and is accompanied by many moults.Sometimes several pupal and larval stages occur. In such cases the metamorphosisis accompanied by the same inner processes as in the Insccta with complete meta-morphosis, i. e. by the breaking up and disappearance of larval organs, and by the forma-tion of the d

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