. Amphioxus and the ancestry of the vertebrates [microform]. Vertebrates; Chordata; Fishes; Ascidiacea; Vertébrés; Cordés; Poissons; Ascidiacés. 'OGLOSSfS. 247 Far from assuming as a self-evident fact that the extreme metamerism of the Annelids and Arthropods is genetically identical with that of the Vertebrates, we have every reason to suppose that it has been elaborated entirely independently in the two cases, and that the apparent simi- larity is due, as already intimated, to a />am//e-/ evolution. Body-cavities ; Proboscis-pore; Collar-pores. Corresponding to the three regions in
. Amphioxus and the ancestry of the vertebrates [microform]. Vertebrates; Chordata; Fishes; Ascidiacea; Vertébrés; Cordés; Poissons; Ascidiacés. 'OGLOSSfS. 247 Far from assuming as a self-evident fact that the extreme metamerism of the Annelids and Arthropods is genetically identical with that of the Vertebrates, we have every reason to suppose that it has been elaborated entirely independently in the two cases, and that the apparent simi- larity is due, as already intimated, to a />am//e-/ evolution. Body-cavities ; Proboscis-pore; Collar-pores. Corresponding to the three regions into which the body of Balanoglossus is divided, — namely, probos- cis, collar, and trunk, — the body-cavity is divided up into three systems of cavities. These are (a) the anterior body-cavity or cavity of the proboscis, (/3) a pair of collar- cavities, and (7) a pair of body-cavities which form the unsegmented coelom of the trunk (Figs. 114, 115). These cavities arise essen- tially as pouches from the archenteron (Fig. 117), al- though their actual develop- ment differs considerably in different species (Morgan). The proboscis-cavity is placed in communication with the exterior by an open- ing through the posterior 'I'.' Fig. 116. — Diagram of the organisa- tion of Balanoglossus, from side. (From a drawing kindly lent by Professor 'I'. H. Mokcan.) Collar-pores. ^^^). Gonads, Gill-slits; the dark lines converging he- hind indicate the superficial pcirtions of the gill-slits; below the surface are seen the free ends of the toneue-bars. //. igut cis-pore. Other letters as abovi. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Willey, Arthur, 1867-1942. New York; London : Mcmillan
Size: 933px × 2678px
Photo credit: © Library Book Collection / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1800, bookdecade1890, booksubjectfishes, bookyear1894
