. A textbook of invertebrate morphology [microform]. Invertebrates; Morphology (Animals); Invertébrés; Morphologie (Animaux). TYPE MOLLUSC A. 363 Qtle and r a thin of those [i yolk, in modified, ems clear, ence of a stry of the t in forms ipe of the 3sts forms tocardiate doubt but is they do primitive ent of the le ctenidia tion. The the Octo- the former 1 called to to the An- d out that n ancestor inderstand imilarities, ia, but ex- o respects, ophore; it eadily ex- ures origi- lal—a plic- admittod, icemen t are nphineura. le former a ^nized. If ited that it, than in the lilar struct- !y acqu
. A textbook of invertebrate morphology [microform]. Invertebrates; Morphology (Animals); Invertébrés; Morphologie (Animaux). TYPE MOLLUSC A. 363 Qtle and r a thin of those [i yolk, in modified, ems clear, ence of a stry of the t in forms ipe of the 3sts forms tocardiate doubt but is they do primitive ent of the le ctenidia tion. The the Octo- the former 1 called to to the An- d out that n ancestor inderstand imilarities, ia, but ex- o respects, ophore; it eadily ex- ures origi- lal—a plic- admittod, icemen t are nphineura. le former a ^nized. If ited that it, than in the lilar struct- !y acquired should be kept in mind, especially in view of another idea as to the gene- alogy of the Mollusca which has been advocated by certain authors Ac- cording to this theory they have sprung from Turbellarian-like ancestors the creeping surface of the worm having become more muscular, and so having given rise to the foot of the MoUusk, the dorsal region of the body elevat ing into the visceral hump. The nervous system of the Amphineura, with Its ladder- Ike arrangement, miglit readily be deduced from the arransre- inen found in the Platyhelminths, and thus many points on which the Tro- chophore theory throws no light become intelligible. This tlieory concerns itself mainly with tlie adult forms, yet it is not unpossible that a reconciliation between it and theTrochophore theory mar be possible. It has already been pointed out that the Trochonhore mav possibly be the representative of a Turbellarian larva, and the same idea may be applied to the Veliger. In other words, it is possible that the Mollusca may have been derived from the Turbellaria, and that the ances tral worms possessed in tlieir life-history a larva whicli, independently of the adults, underwent a series of modifications leading to the Veliger The Vehger would then be the descendant of a Turbellarian la'-va while the adult xMollusk would be directly descended from the Turbellarian This view may be contrasted w
Size: 1619px × 1544px
Photo credit: © The Book Worm / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1800, bookdecade1890, bookpublishernewyo, bookyear1896
