G40 MUSCULAR TISSUES IN HYDROID POLYPS. 



muscular layer, then the stalks of the epithelial cells move upward 

 and finally occupy the ridges which have been formed, whilst the 

 muscular cell adhering closely to the supporting lamella forms a 

 continuous layer on the sides and at the bottom of the valley. The 

 nervous elements which always lie above the muscular layer of 

 course, then fill the part of the valley which has not been 

 occupied by the muscular elements. In the case of the tentacles 

 of some Actinge indifferent tissue is formed between the muscular 

 and nervous layers (1.) 



Such structures, however, appear rare, and have, as far as I 

 know, not been observed anywhere else. A muscle, such as that 

 described above of Sarsia radiata, however, is a structure very 

 similar to that in other Coelenterata \ also here the same causes 

 have produced the same effect independently of each other. 



Explanation of Plate XXX. 

 Sarsia radiata. 



Fig. 1. — Transverse section through the base of a Hydranth. L. Oc. I. 

 Fig. 2. — Three Hydranths in different positions. 



a. — bent down half. 



b. — erect. 



c — bent down quite. 

 Fig. 3. — Longitudinal section through the basal portion of the Hydranth 

 along the plain in which the Hydranth bends. DD. Oc. I. 



S. layer of Chitin in the Perisarc. 

 Fig. 4. — Transverse section through the base of the Hydranth. DD. Oc. I. 



M. Muscuhis Flexor. 



(1) Von Lendenfeld. Zur Histologic der Actinien, Zoologisher .Anzeiger. 

 Band VI. Seite 189. 



