Life And Rock: a Collection of Zooogical And Geological Essays
The book Life And Rock: a Collection of Zooogical And Geological Essays was written by author Richard Lydekker Here you can read free online of Life And Rock: a Collection of Zooogical And Geological Essays book, rate and share your impressions in comments. If you don't know what to write, just answer the question: Why is Life And Rock: a Collection of Zooogical And Geological Essays a good or bad book?
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69 tooth-germs. It has been shown, indeed, that the teeth in the latter part of the series, when first formed, consist of a number of adjacent cusps, and that as development proceeds these cusps become completely separated from each other so as to constitute distinct individual teeth of a simple conical form. This discovery is of the very highest import, since it serves to indicate how the numerous simple conical teeth of the dolphins and other toothed whales have probably been derived by the s...plitting and subdivision of originally complex cusped teeth more or less closely resembling those of the extinct zeuglodonts referred to in the last chapter. Being primarily distinguished from the toothed whales oy the total absence of teeth after birth and the presence of whalebone in the adult condition , the whalebone whales present certain other distinctive characters to which we may now briefly allude. In the first place, the whales of this group differ externally from all those furnished with teeth in that their nostrils open externally by two distinct longitudinal slit- like apertures ; while, if we cut into the head, we shall find that there is a distinct organ of smell, of which all traces have disappeared among the toothed whales.
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