i66 



ACTINIARIA 



Fig. 172 



The structure of the sphincter varies from palmate to pinnate, and affords no good character neither 

 of the species nor of the genus. 



The longitudinal muscles of the tentacles are mesogloeal, as already observed by O. and R. Hertwig 

 1879. They, however, show a certain variation, in as much as they are now ecto-mesogloeal now meso-ecto- 

 dermal. It was therefore formerly supposed that the mesogloeal tentacle nmscles were characteristic of 

 Urticina felina coriacea. In fact the variation is still greater, as I have in small, but sexually ripe specimens 

 found a perfectly ectodermal longitudinal muscularity of the tentacles. I haveinthetextfigure 171 reproduced 

 a transverse section of part of the tentacular muscles and the mesogloea of one of the below named specimens 

 from Hellebsek, which certainly is a real U. felina coriacea. The specimen has namely well-developed verrucae, 

 its sphincter is palmate, the mesenteries show the arrangement, characteristic of Urticina, and the nemato- 



cysts in the actinopha- 

 rynx and tentacles agree 

 with those of this species. 

 For comparison I have 

 in the textfigures 173, 174 

 reproduced transversal 

 sections of two pieces of 

 tentacles of an Urticina 

 from Heligoland. On one 

 piece we find a compara- 

 tively thin mesogloeal la- 

 mella outside of the ra- 

 ther fine muscle meshes, 

 the part of the mesogloea 

 facing the ectoderm here 

 and there displays distinct muscles. On the other piece the comparatively few meshes are found wholly 

 within the mesogloea ; whether there are muscles to be found also on the ectodermal side, I will leave un- 

 decided, as, upon all accounts, if present they are ver^^ weak. The two latter figures have been reproduced 

 from the same section, which shows that the variation is very great at the same level of a tentacle. The 

 longitudinal muscles of the tentacles of Urticina thus vary from ectodermal to ecto-mesogloeal, possibly to 

 wholly mesogloeal. 



The radial muscles of the oral disc agree with the longitudinal muscles of the tentacles. I have before 

 (1893) shown that they are ecto-mesogloeal or perhaps more correctly meso-ectodermal. In the textfigure 

 172 part of a transverse section through the oral disc of the above named specimens from Hellebaek has been 

 reproduced. As we see, the radial muscles are ectodermal. 



Thus longitudinal muscles of the tentacles and the radial muscles of the oral disc vary from ecto- 

 dermal, in smaller but sexually ripe specimens, to more or less mesogloeal, in middle-sized and large specimens. 

 In other words, the folding of the ectodermal muscle lamella into the mesogloea, or tlie fusion of the peripheric 



Textfigs. 171 — 174. 



Urticina felina coriacea. 



Figs. 171, 173, 174 Transverse sections of a part of 



some tentacles. Fig. 172 Transverse section of a part 



of the oral disc. Figs. 171, 172 spec, from Hellebaek, 



figs. 173, 174 spec, from Helgoland. 



