Chap. I. HISTORY OF THE ACALEPHS. 31 



strates beyond the po,s.sil)ilit_y of a doubt, that the Scyphistomas are the oflsprinf 

 of Medusa; ; that they are transformed mto Strobihx;, Avhich produce Ephj-roid 

 Medusa3 ; and that the Litter end their hfe as Medusa aurita and Cyanea capiUata. 

 All these facts are illustrated by beautiful figures. He begins by showing that the 

 free disks of his Strobila are the young Medusa (Aurelia) aurita. He next instances 

 fiicts showing the similarity of the development of Cyanea capillata with that of 

 Aurelia aurita ; and then describes his attempts to raise the eggs of the Medusse, 

 in which he succeeded so fixr as to show that Scyphistomas are developed from 

 eggs laid by l:)oth these Medusa;, and thus closes the cycle of the investigation 

 undertaken with the A'iew of ascertaining the normal connection of all these animal 

 forms. There can no longer be any doubt that they are genetically linked together, 

 even though the transformation has not been watched through all its stages m one 

 and the same specimen. The difficulty of keeping them alive for a sufficient time 

 in confinement makes it impossible to obtain that kind of evidence. But as far as 

 the closest similarity of the forms watched in confinement with tliose oljserved in 

 their natural element is sufficient to trace their mutual dependence, the evidence 

 is satisfactory and conclusive.^ 



The investigations of Sars had scarcely begun to be noticed in Germany when 

 Sieljold proceeded to trace the earliest stages of the formation of these animals." 

 His object was jiartly to revise the observations of Ehrenberg upon the structure 

 of the Aureha aurita, and partly to study the develojiment of its eggs. To him 

 we are indebted for the first accurate observations respecting the segmentation of 

 the egg, and the formation of the embryo. Siebold clearly perceived the connection 

 of the facts he had observed with those seen by Sars, yet a direct transition of 

 the young from the state to which he had traced it to that observed by Sars 

 was not seen by him. 



The successive discoveries of Sars, combined with the investigations of von 

 Siebold, had already led to a full knowledge of the characteristic features of the 

 mode of development of the Meduste, when Steenstrup took up this subject; and 

 yet this ingenious observer gave a new imi^ulse to the investigation of the Aca- 



j)l. 1-4. — A French translation, by Dr. Young, in Wiegm. Arch. 1841, I. p. 20. 2(1, The base of 



appeared in the Annales des Sciences naturelles, the StroI>ihi, after the Ephyra? are freed, does not 



2d series, 1841, vol. IG, p. 321. die, as Sars states. Dalyell is correct when he 



^ There are, however, two assertions in this affirms that they survive, and that tentacles reappear, 

 paper with which I cannot coincide: 1st, the re- ^ Siebold (C. Th. vox), Beitriige zur Natur- 



versal of the young embryo when it becomes attached. gesehichte der wirbellosen Thiere ; Neueste Schrif- 



Notwithstanding the objections of Sars, Siebold was ten der naturforschenden Gesellschaft in Danzig, 



right in what he said of tlie formation of the vol. 3d, No. 2, Danzig, 1839. 

 mouth, though he gave it up afterward. See note 



