MUSCULAR TISSUES IN HYDROIDS POLYPES. 

 By R. von Lendexfeld, Ph.D. 



Plate XXX. 



The muscular tissue of the Ccelenterata is produced like that 

 of all Metozoo from the two germinal layers of the gastrula 

 embryo. In some of the orders this process is carried out direct ; 

 the muscles are epithelial. In others the muscles are pro- 

 duced from the Mesoderm, and therefore do not appear epithelial. 

 The Hydromedusae, Syphonophora, Schyphomedusa?, and Antozoa 

 belong to the first group. The muscular fibres at first appear 

 as processes of the centripetal part of the epithelial cells (1) 

 with higher development division of labour occurs; some of the 

 epithelcells lose whilst others retain the locomotory function. At 

 the same time the muscular cells reti-eat from the surface, which is 

 finally exclusively formed by the non-muscular covering cells. The 

 muscular cells and their fibres form a layer between the Mesoderm 

 (Stiizlamelle) and the covering Epithelium (2.) The shape of the 

 muscular lamella obviously depends on the shape of the supporting 

 membrane. As long as the latter remains simple and unfolded, 

 the muscular lamella cannot attain a higher degree of development. 

 This is, however, achieved in many cases in the following manner : 

 — The supporting lamella forms longitudinal ridges, and in this 



(1) N. Kleinmberrj. Hydra, Leipzig, 1872. Seite 15. 



(2) 0. und B. Hertifig. Die Actinien. Jenaische Zeitschrift. Band XIV., 

 Seite 47. 



