. The Cambridge natural history. Zoology. 136 URODELA either capable of loug fasts or live ou infusoria in the ; It seems more reasonable to suppose that tliese newts live upon Cnistacea, four kinds of which, all new to science, also came up with the water. Fam. 4. Sirenidae.—Tlie three pairs of fringed external gills persist throughout life. The body is eel-like. Hind-limbs are altogether absent, while the fore-limbs are short and have three or four fingers. The maxillar}' bones are absent. "With the exception of small teeth on the vomer the mouth is tooth- less, but the jaws
. The Cambridge natural history. Zoology. 136 URODELA either capable of loug fasts or live ou infusoria in the ; It seems more reasonable to suppose that tliese newts live upon Cnistacea, four kinds of which, all new to science, also came up with the water. Fam. 4. Sirenidae.—Tlie three pairs of fringed external gills persist throughout life. The body is eel-like. Hind-limbs are altogether absent, while the fore-limbs are short and have three or four fingers. The maxillar}' bones are absent. "With the exception of small teeth on the vomer the mouth is tooth- less, but the jaws are furnished with horny sheaths. The eyes are devoid of lids, but shine through the skin. The Sirenidae are the most degraded members of the Urodela and are represented by two closely-allied genera, each with one. Fig. 27. Siren lacertina. >: '.. species, in the south-eastern parts of the United States. Their most interesting feature, which bears upon the cjuestion of neoteny, is their retrograde metamorphosis as descriVjed by Cope.^ The gills atrophy in the young and are subsetj^uently redeveloped. Cope therefrom concludes rightly that the ultimate or persistent gills of Siren are signs of maturity and not a larval character. In young specimens of Siren of 5 to 6 inches in length tlie gills are functionless: in one of 3 inches they were found to be entirely vestigial and " subepidermal," covered by a common dermal investment. Unfortunately really young larvae are still unknown. Old Sirens can li\e witliout gills, as has been shown by acpiarium-specimens. In the adult Psevdo- hntnchus all the gills are normally covered up by an investment of the skin so as to be quite without function and movability. Siren loeertina, the " mud-eel," is distinguished by the ' Amrr. Xnluml. xix. 18S5, p. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of the
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