. The advancement of science. Occasional essays & addresses. Natural history. 36 DEGENERATION : perhaps most distinctive and clinching as an evidence of affinity, the myelonic or cerebral eye. Now let us convince ourselves that these four features exist not only in the frog's tadpole, as they do in all fishes, reptiles, birds, and beasts, but that they also exist in the Ascidian tadpole, and, it may be added, coexist in no other animals at all. The corresponding parts are named in Figs. 16 and 17, in such a way as to render their agreement tolerably clear, whilst in Fig. 18 a more detailed
. The advancement of science. Occasional essays & addresses. Natural history. 36 DEGENERATION : perhaps most distinctive and clinching as an evidence of affinity, the myelonic or cerebral eye. Now let us convince ourselves that these four features exist not only in the frog's tadpole, as they do in all fishes, reptiles, birds, and beasts, but that they also exist in the Ascidian tadpole, and, it may be added, coexist in no other animals at all. The corresponding parts are named in Figs. 16 and 17, in such a way as to render their agreement tolerably clear, whilst in Fig. 18 a more detailed representation of the head of an Ascidian tadpole is Fig. 18.—Ascidian Tadpole with a part only of the tail C. X, nervous system with the enlarged brain in front and the narrow spinal chord behind {n); N', is placed in the cavity of the brain ; 0, the single cerebral eye lying in the brain ; a, similarly placed auditory organ ; AT, pharynx ; d, intestine ; o, rudiment of the mouth ; ch, notochord or primitive backbone. (From Gegenbaur's Elements of Comparative Anatomy.) It is clear then that the Ascidians must be admitted to be Vertebrates, and must be classified in that great sub-kingdom or branch of the animal pedigree. The Ascidian tadpole is very unlike its parent the Ascidian, and has to go through a process of degeneration in order to arrive at the adult structure. The diagrams which are reproduced in Figs. 19 and 20 show how this degeneration proceeds. It will be observed, that. 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 Lankester, E. Ray (Edwin Ray), Sir, 1847-1929. London and New York, Macmillan
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