. Zoology : for students and general readers . Zoology. 314 ZOOLOGY. step upwards. Dana's law of cephalization, or transfer of parts headwards, is more strikingly manifested in the Crus- tacea than in any other animals. Nearly all Decapods undergo this decided metamorphosis ; in only a few forms, such as the craw â fish, lobster, and a few shrimps and crabs, do the young leave the egg in the general form of the adult, the Zoea stage being rap- idly assumed and dis- carded during em- bryonic life. Most Crustacea bear their eggs about with them ; in only a few cases, as the Squilla and the land-
. Zoology : for students and general readers . Zoology. 314 ZOOLOGY. step upwards. Dana's law of cephalization, or transfer of parts headwards, is more strikingly manifested in the Crus- tacea than in any other animals. Nearly all Decapods undergo this decided metamorphosis ; in only a few forms, such as the craw â fish, lobster, and a few shrimps and crabs, do the young leave the egg in the general form of the adult, the Zoea stage being rap- idly assumed and dis- carded during em- bryonic life. Most Crustacea bear their eggs about with them ; in only a few cases, as the Squilla and the land-crab of the West Indies, are the eggs left by the j)arent in holes or on the sea-shore. The Decapoda are divided into the 8cliizopoda, repre- sented by Mysis; the Cumacea, repre- sented by Giima ; the long-tailed Decapods, such as the shrimps and lobster, called Macrura, and the genuine short-tailed Decapoda, or Bra- chyura. Most of the species of the crabs are confined to tropical seas and live in shallow water. The Decapods appeared in the Coal Period, and were rep- resented by somewhat generalized , such as Anthra- palmmo'ii (Pig. 267) from the coal measures of Illinois. Eecently a genuine crab {Brachyinjge carbonis) has been described by Woodward from the carboniferous formation of Belgium. Crustacea, especially shrimps and crabs, are sensitive to. Fig. 206.âMegalops of the Crab.âAfter 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 Packard, A. S. (Alpheus Spring), 1839-1905. New York : Henry Holt
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Keywords: ., bookcentury1800, bookdecade1870, booksubjectzoology, bookyear1879
