. Amphioxus and the ancestry of the vertebrates [microform]. Vertebrates; Chordata; Fishes; Ascidiacea; Vertébrés; Cordés; Poissons; Ascidiacés. mm'^^ 246 T//£ PA' O TO CIIQRDA TA. «: i m. il I II'. Fig. 115. — Diagrammatic transverse sec- tion through hinder region of proboscis of Balanoglossus. (From a drawing kindly lent by Professor T. H. MORGAN.) D. Dorsal. V. Ventral, bc"^. Proboscis- cavity, almost filled up by mesenchymatous and muscular tissue* proliferated from the original coelomic Lpithelial layer (indicated by the black line below the ectoderm). Pulsating vesicle, h. Hea
. Amphioxus and the ancestry of the vertebrates [microform]. Vertebrates; Chordata; Fishes; Ascidiacea; Vertébrés; Cordés; Poissons; Ascidiacés. mm'^^ 246 T//£ PA' O TO CIIQRDA TA. «: i m. il I II'. Fig. 115. — Diagrammatic transverse sec- tion through hinder region of proboscis of Balanoglossus. (From a drawing kindly lent by Professor T. H. MORGAN.) D. Dorsal. V. Ventral, bc"^. Proboscis- cavity, almost filled up by mesenchymatous and muscular tissue* proliferated from the original coelomic Lpithelial layer (indicated by the black line below the ectoderm). Pulsating vesicle, h. Heart, ch. Noto- chord. Integumentary nerve-plexus. The genital organs, testes or ovaries, accord- ing to the sex of the individual, occur as a paired metameric series of pouch-like bodies or gonadic sacs which ex- tend backwards far be- yond the region of the gill-slits. The gonadic sacs are suspended in the body-cavity by solid cords attached to the dorsal integument, which be- come perforated in the spawning season to ad- mit of the expulsion of the reproductive elements. Metamcj'ism. Although there is no muscular metamerism in Balano- glossus, yet we have seen that other organs (gill-slits and gonads) are arranged metamerically. And in point of fact, among those Invertebrates which are not included under the phylum of the Articulata, if there is one pecu- liarity of organisation more sporadic in its occurrence than another, it is metamerism. It may affect the most differ- ent organs of the body either collectively or individually, and nothing is more patent than the fact that the meta- meric repetition of parts has arisen independently over and over again in different groups of animals.^ * This tissue is not represented in Figs. 114 and 116, although it is present throughout the 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
Size: 1577px × 1585px
Photo credit: © Library Book Collection / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1800, bookdecade1890, booksubjectfishes, bookyear1894
