. Animal activities; a first book in zoo?logy. Zoology; Animal behavior. HOMOLOGIES AMONG CRUSTACEA. 109 frequently happens that animals bearing only slight external resemblance to one another in adult life are classified together because in embryological life they show so many resem- blances. Among the ten thou- sand or more species of Crustacea, there are many strange forms which de- part from what might be called the typical crusta- cean structure. Compar- ing the common crab (Cancer irroratus) with the shrimp or crayfish, we notice the small size of the abdomen folded under the flattened c
. Animal activities; a first book in zoo?logy. Zoology; Animal behavior. HOMOLOGIES AMONG CRUSTACEA. 109 frequently happens that animals bearing only slight external resemblance to one another in adult life are classified together because in embryological life they show so many resem- blances. Among the ten thou- sand or more species of Crustacea, there are many strange forms which de- part from what might be called the typical crusta- cean structure. Compar- ing the common crab (Cancer irroratus) with the shrimp or crayfish, we notice the small size of the abdomen folded under the flattened carapace. In the hermit crab the abdo- men is soft and has lost part of the swimmerets, be- cause of its habit of using the shell of a snail for pro- tection, yet in the young the abdomen of this animal. Fig. 96. Water-flea {Dafhnia pulex).. 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 French, Nathaniel Stowers, 1854-. New York [etc. etc. ] Longmans, Green and Co
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