MARINE ANIMALS OF MASSACHUSETTS BAY. 



ON RADIATES IN GENERAL. 



IT is perhaps not strange that the Radiates, a type of animals 

 whose home is in the sea, many of whom are so diminutive in size, 

 and so light and evanescent in substance, that they are hardly to 

 be distinguished from the element in which they live, should have 

 been among the last to attract the attention of naturalists. Nei- 

 ther is it surprising to those who know something of the history of 

 these animals, that when the investigation of their structure was 

 once begun, when some insight was gained into their complex life, 

 their association in fixed or floating communities, their wonder- 

 ful processes of development uniting the most dissimilar individ- 

 uals in one and the same cycle of growth, their study should have 

 become one of the most fascinating pursuits of modern science, 

 and have engaged the attention of some of the most original in- 

 vestigators during the last half century. It is true that from 

 the earliest days of Natural History, the more conspicuous and 

 easily accessible of these animals attracted notice and found their 

 way into the scientific works of the time. Even Aristotle de- 

 scribes some of them under the names of Acalephae and Knidae, 

 and later observers have added something, here and there, to our 

 knowledge on the subject; but it is only within the last fifty 

 years that their complicated history has been unravelled, and the 

 facts concerning them presented in their true connection. 



Among the earlier writers on this subject we are most indebted 

 to Rondelet, in the sixteenth century, who includes some account 

 of the Radiates, in his work on the marine animals of the Medi- 

 terranean. His position as Professor in the University at Mont- 

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