Elementary text-book of zoology (1884) Elementary text-book of zoology elementarytextbo0201clau Year: 1884 TETHYODEA. 95 into a long nerve, which at the base of the tail dilates to a ganglion, and in its further course forms a number of smaller ganglia (tig. 563). The reduction of the central nervous system to the simple ganglion of the Ascidian begins after loss of the tail, and after development of the branchial basket. Of sense organs the processes of the integument which serve for tactile purposes (the lobes of the oral and at rial apertures and the tentacles), and peripheral nerves, endi
Elementary text-book of zoology (1884) Elementary text-book of zoology elementarytextbo0201clau Year: 1884 TETHYODEA. 95 into a long nerve, which at the base of the tail dilates to a ganglion, and in its further course forms a number of smaller ganglia (tig. 563). The reduction of the central nervous system to the simple ganglion of the Ascidian begins after loss of the tail, and after development of the branchial basket. Of sense organs the processes of the integument which serve for tactile purposes (the lobes of the oral and at rial apertures and the tentacles), and peripheral nerves, ending in epithelial cells, are most widely distributed. The large ciliated cells on the edge of the mouth of the Copdata must be placed in the same category. The ciliated pit is to be regarded as an olfactory organ. It consists of a depression in the wall of the pharynx lined with ciliated cells, and is situated in front of the ganglion. Accord- ing to Julin, it is, to- gether with a gland situated beneath the ganglion, to be regarded as the equivalent of the hypophysis. In the Copdata the ciliated pit is elongated and lies on the right side of the ganglion. There is an auditory vesicle on the left side of the ganglion in the Copdata. This structure, which is developed from a cell of the of the ganglion, is found in the Ascidian larvae, but degenerates soon after the attachment of the larva. Paired auditory vesicles appear in Pyrosonm where they are connected with the ganglion by a short stalk. Masses of pigment which are present with great regularity on the lips of the large openings of the body in the simple and compound Asciclians may be interpreted as eye spots. The eye of the Ascidian larvse, which lies on the ganglion and originates from a part of the neural canal, has a more complicated structure. Later it degenerates, but in Pyrosoma it is retained in the adult condition and possesses a lens-like structure. FIG. 563.—Xervous system of A/i/fOx/.V,'/ rcata (after Fol.).
Size: 1382px × 1447px
Photo credit: © Bookworm / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: archive, book, drawing, historical, history, illustration, image, page, picture, print, reference, vintage
