TABLE OF CONTENTS. 



PART I . 



ACALEPHS IN GENERAL. 



CHAPTER I 



HISTORY OF OUR KNOWLEDGE OF THE ACALEPHS. 



Section 1. Period of Aristotle and the Roman natu- 

 ralists. — We find unquestionable evidence in Aiistotle's 

 History of Animals that he knew the Radiates now 

 called Acalephs by systematic writers, though this name 

 was applied by the ancient Greeks to the Actinite as 

 well as to the Acalcphse of zoologists. Phny added 

 nothing to the information of his predecessors, except 

 a few remarks on the movements of the Medusa?, 

 p. 3-7. 



Sectiox 2. The naturalists of the sixteenth and seven- 

 teenth centuries. — Kondelet is the chief investigator of 

 this period ; his observations on Medusa; disclose the 

 same accuracy of observation and the same penetration 

 as his other investigations on all the natural productions 

 of the Mediterranean. Gessner deserves to be studied 

 chiefly on account of his great erudition, and Rondelet 

 for his deep insight into the relations of animals, p. 7-12. 



Section 3. The naturalists of the eighteenth century. — 

 Linnajus gives character and importance to the study 

 of Natural History, by the publication of the " Sys- 

 tema Naturaj." His pupils and followers explore the 

 world in every direction, p. 13-18. 



Section 4. The systematic writers and anatomists.- — In 

 the beginning of the nineteenth centm-y the Acalephs 

 begin to be made the subject of special investigations. 

 Peron and LeSueur, and, twenty-five years later, Esch- 

 scholtz, mark two gi'eat epochs in this pi-ogress. p. 18-27. 



Section 5. Emhryological researches upon Acalephs. — 

 The investigations which have led to the knowledge 

 of the modes of reproduction and growth of the Aca- 

 lephs are among the most interesting ever made by 

 naturalists. Sars and Steenstrupp are most prominent 

 among the discoverers in this field, and, next to them. 

 Siebold, Dalyell, and Dujardin. p. 28-3-5. 



CHAPTER II. 



ACALEPHS AS A CLASS. 



Sectiox 1. ISIode of determining the natural limits of 

 the class. — The study of the structure of animals, unless 

 combined with a knowledge of their mode of develop- 

 VOL. III. B 



ment and of their homologies, is not sufficient to trace 

 the natural hmits of the classes, p. 3G-40. 

 Section 2. The different animals referred to the ti/pc 



