Chap. I. HISTORY OF THE ACALEPIIS. 35 



Quatrefagcs,^ -without leading to conclusive results, when Dujardin turned his atten- 

 tion to the subject, and published two most important papers^ describing the 

 formation of genuine Medusaa from Hydroids ; and thus establishing beyond question 

 a genetic relation between animals of another family which had thus far been 

 considered as belonging to different classes. Dujardin's investigations had a great 

 influence in establishing the correctness of the views of Sars and Steenstrup, and 

 in extending the range of our knowledge of the alternate generations ; for, not only 

 did he trace the development of several Medusae from Hydroid Polyps, but he even 

 saw the eggs of the free Meduste derived from Hydroids reproduce their Hydroids. 

 His second paper is accompanied by many Ijeautiful figures, which add greatly to 

 the clearness of his descriptions, and have forced the facts more directly upon the 

 attention of naturalists. 



Henceforward the study of the Acalephs is pursued in a new light and with 

 broader views. The investigation of their affinities, their structure, and their mode 

 of development, forms a part of their history ; and their classification is modified 

 accordingly, and gradually brought nearer and nearer to nature. 



' QuATREFAGES (A. de), Memoire sur la Syn- veau genre de Mcdusaires {Cladonema) provenant 



hydre jiarasite {Synhydra parasites), nouveau genre de la metamorphose des Syncorynes; Ann. Sc. Nat. 



de Polype voisin des Hydres ; Ann. Sc. Nat. 2de 2de ser. 1843, vol. 20, p. 370. — Memoire sur le 



ser. 1843, vol. 20, p. 230. developpement des Medusaires et des Polypes Hy- 



- DujAKDiN (Fel.), Observations sur un nou- draires ; Ann. Sc. Nat. 3e ser. 1845, vol. 4. p. 257. 



