Dr. A. Korotncff ow Polypariura ambulans. 213 



terrupted layer of fibres, which commence at the buccal disk, 

 where the septa are inserted, and extend thence downwards, 

 to lose themselves in the foot-disk. The transverse muscles, 

 on the contrary, are the strongest, and form strong bundles of 

 fibres, which run from one side of the body of the Polyparium 

 to the other. Fig. 2 shows how strongly the transverse 

 muscles are developed ,• immediately behind the buccal aper- 

 ture they form a large cushion {t. F), which projects far into 

 the interior chamber, nearly meeting with the cushion of the 

 opposite side. The cushion, however, stops in the middle of 

 the septum, being sharply separated by a constriction from 

 the septum, which now becomes thinner. The inferior half 

 of each septum is clothed with a single layer of transverse 

 fibres, and this lines the inner surface of the so-called stoma- 

 chal cavity, which, as already stated, penetrates into the 

 interior of each acetabulum. The whole surface of the 

 muscles is covered with a single-layered entoderm (fig. 9), 

 which, at the bottom, contains the strongly developed mus- 

 cular fibres imbedded in a common plasma. 



On examining into the peculiarities of this structure it 

 appears that its greatest divergence from the polyp-type con- 

 sists in the entire absence of strongly developed bands of 

 muscular bundles in Polyparimn. But if we consider that 

 the muscles on the one hand are in relation to the tentacles, 

 and on the other serve for the retraction of the whole buccal 

 disk into the interior of the body of the Actinia, it becomes at 

 once quite intelligible to us that such bands are wanting in 

 Polyyarium as being superfluous, for no tentacles are present, 

 and from the great number of small buccal orifices the buccal 

 disk cannot be retracted. Nevertheless there is a point of 

 argument which may enable us to establish an analogy ; thus 

 the vertical muscles, arranged in a thin fibrous layer, which 

 line the intermediate chambers are homologous with the true 

 muscular bands. Thus in Polyparium we find a reversed 

 picture with relation to the polyps ; the vertical fibres, which 

 are the strongest in the polyps, are the least strongly deve- 

 loped in Polypariam^ and vice versa the transverse fibres are 

 the strongest in Polyparium, and may therefore be charac- 

 terized as "transverse bands (transversale Fahnen) ^ 



In order to find something similar among the polyps we 

 must go back to the statements of Hollard *. That naturalist 

 first of all described a parieto-basilar muscle in the Actinise ; 

 this muscle consists of fibres which run from the wall- 

 lamina to the pedal disk to draw in the latter ; it appears 



* " MoDOgrapliie anatomiqiie du genre Actinia de Linn^," &c., in 

 Ann. Sci. Nat. Zool. s6r. 3, tome xv. p. 257. 



