THE 



VOYAGE OF H.M.S. CHALLENGER, 



ZOOLOGY. 



REPORT on the Actiniaria dredged by H.M.S. Challenger during the 

 years 1873-187G. By Prof. Richard Hertwig. 



INTRODUCTION. 



In investigating the Anthozoa the majority of earlier naturalists were content to give 

 the most exhaustive description possible of the parts which are externally visible in the 

 living animal, and of the skeleton where such a structure existed ; on the other hand, 

 they only went slightly into more exact anatomical details, as the observation of 

 these presented great difficulties. The majority of the Anthozoa are not sufficiently 

 transparent to allow of the recognition of the form and arrangement of the organs in the 

 living animal, whilst after death they are so contracted that all the parts become mis- 

 placed in many ways and pressed one against the other, and can only be demonstrated, 

 with great care, by means of knives and scissors. Up to the present time the systematic 

 survey and characters of the orders, families, and genera are founded upon external 

 characteristics which are of less morphological importance. 



In this way many errors arose, which have only become intelligible from the 

 work of the last decades. Following the steps of Agassiz (Contrib. to the Nat. Hist. 

 of the United States, vol. iii.), Moseley (Phil. Trans., vol. clxvi. pt, 1, p. 91, 1876; vol. 

 clxviii. pt. 2, p. 425, 1878) has shown in the most convincing fashion that many hydroid 

 polyps which form skeletons have been long placed among the reef-forming corals, and 

 that, moreover, in consequence of the skeletal formation alone having been taken into 

 consideration, many Octocorallia have been disconnected from their natural systematic 

 place, and united to forms entirely remote. It cannot by any means, be asserted that 



^"(ZOOL. CHALL. EXP.— PART XV. 1882.) P 1 



