AND THE LOWER ANIMALS. 149 



Chainisso, less fortunate than Peysonnel, died, not 

 only before his opinions had received recognition, but 

 even without having himself understood the immense 

 importance of his discoveries. 



Chamisso's observations, at first certainly incom- 

 prehensible, and those, still more obscure, announced 

 by Carus, in 1818, as the result of his researches on the 

 HelmintheSj or intestinal worms, marked an entirely new 

 era in the history of development. By these pioneers 

 a path was thrown open, along which we travel every 

 successive day with more and more security, but in 

 which it is also possible to lose the right track, and 

 thus commit serious errors. The entire history of 

 these explorations, made to determine the proper 

 route, is pregnant with interest, but it would occupy 

 far too much space, and is of too difficult a nature, 

 for us to pursue it. We must, therefore, confine 

 ourselves to setting down the landmarks, as it were, 

 of the paths traced by those who first visited this 

 "unknown land; ;; * and in doing so, we shall occa- 

 sionally be obliged to invert the chronological order of 

 the discoveries, in order to present the reader at first 

 with the typical results. Under the latter category 

 the works of Saars and Charles von Siebold, on the 

 reproduction of Medusas, occupy unquestionably the 

 first rank. 



We shall now detail certain facts which, though 

 well known to all naturalists, are unfamiliar to most 

 of our readers. 



For almost half a century, the classes Acalephce 

 and Polyps have held a place among the other 



* An expression employed by Siebold, to designate especially 

 the history of the reproduction of the Helminthes. 



