File:Guide leaflet (1901) (14581557359).jpg

Identifier: scienceguide7692amer (find matches)
Title: Guide leaflet
Year: 1901 (1900s)
Authors: American Museum of Natural History
Subjects: American Museum of Natural History Natural history
Publisher: New York : The Museum
Contributing Library: American Museum of Natural History Library
Digitizing Sponsor: IMLS / LSTA / METRO

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commercial leather known as ^galuchat isshark skin. Around the mouth of the shark, these denticles becomeenlarged and give rise to the teeth. The swifter sharks, like the Mackerel Shark (Case 11), pursue anddevour live fish, but the more sluggish ones, like the Nurse Shark arecontent with offal. Some with blunt teeth, like the Port Jackson Shark(Case 7), crush shellfish, while some with very large mouths and reducedteeth, such as the Whale Shark (see separate case) and the Basking Shark,(above Case 11), feed like whales on small copepods and other floating,shrimp-like forms. Reproduction: Sharks produce but a few eggs at a time, in contrastto the hundreds of thousands produced by a single Codfish; hence theycan afford, so to speak, to invest a large amount of capital in each egg,that is, to endow the young with a very large yolk. This nourishes theyoung for a long time, so that they are well equipped to take care of them-selves when they are hatched. In some sharks, however, the eggs
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Fig;. 3. Evolution of the Bodj Form of Sharks. 10 THE WOhLI) OF FISHES 11 (levolop within tlic oviducts or (g«i; ducts, and tlic youn^ draw nourish-ment from the mother by means of root-hke outgrowths from the re^;ionof their gills. The Port Jackson Sharks (Heterodontidie). (Case 7;: Duringand before that ancient period of the earths history in which the vastswamps and forests of Pennsylvania were accumulating thcMr stores ofcoal-forming vegetation, the shallow seas of the world swarmed withancient sharks, many of which bore curved spikes on the front marginsof their fins. The more specialized forms of these early sharks becameextinct, but one family survives,—the Port Jackson Sharks—whichare still found living in the Pacific Ocean. These retain the stout finspines and whorl-like crushing teeth of their vastly distant ancestors.They lay eggs which are enclosed in a spirally twisted egg case. The Spined Dogfishes or Squaloid Sharks (Squalidae). (Case 7J:These sharks are far remove

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