BY R. VOX LEXDEXFELD, PH.D. 639 



Similar structures were first observed by Clans (1) in an Apha- 

 cella, and Brothers Hertwig (2) have independently described 

 similar muscles in the Craspedote Medusa?. Identical structures are 

 met with in Actinia?, Acraspedas and Pennatulidee, although they 

 vary very much, still we_find that in so far they resemble one 

 another, that the muscular cells principally cover the lateral 

 surfaces of the supporting ridges, and do not occur on the free 

 margins. Very often they ai*e also wanting in the valley between 

 the supporting ridges. 



Although earlier observers did not take any notice of this fact, 

 still it appears from the figures, that there are no muscles on the 

 free margin of the supporting lamella. In all cases observed by 

 me, the supporting ridges are very thin, the margin of them 

 is continued into the epithelial cells, and I suppose that this 

 pertains also in the cases mentioned above. In every case these 

 muscular bands consist of striated band-shaped fibres as they were 

 first described by Briicke (3.) 



They are attached to a supporting lamella with a narrow side. 



By these facts I have been led to the following explanation of 

 these structures : — The epithelial cells are in connection with the 

 supporting lamella by centrepetal processes. These processes are 

 scattered irregularly over the originally plain surface of the sup- 

 porting lamella. The muscular epithelial cells occupy the spaces 

 between the stalks of the epithelial cells. If the supporting 

 lamella forms folds so that a greater surface is attained to meet the 

 exigencies of the increasing work that has to be done by the 



(1) G. Gmus. Ueber Halestemma tergestinum. Arbeiten aus clem 

 Zoologischen Institute. Wien 1878. Seite 8. 



(2) 0. E. Hertwig. Der Orgauismus der Medusen. 



(3) E. Briicke. Ueber die mikroskopischen Elemente, welcheden Schwim- 

 muskel der Medusa aurita bilden. Sitzngber. A. K. Akademie der Wissen- 

 schaft, Wein. Band. XLVIII. 



