208 Dr. A. KorotnefF on Polyparium ambulans. 



Actinia — that is to say, the sense-fibril (PI. XIII. fig. 7, sf) 

 passes directly or after one division into the nervous layer, 

 with the fibrils of which it perfectly assimilates. I could not 

 observe any sense-hairs upon the ectodermal elements. 



As usual, however, other elements predominate in the ecto- 

 derm, namely the urticating-cells ; but as these scarcely differ 

 from the ordinary type, I have not much to say about their 

 structure. I need only mention that each urticating-cell is 

 suriounded by a thin layer of protoplasm, and that a strongly 

 refractive nucleus is to be found at the bottom of each cell. 

 A fibril is given off downwards from the nematocyst, which 

 passes through the whole ectodermal layer, and is attached 

 by a thickening or disk to a muscular fibril (fig. 7). 



The above-mentioned superior aggregation of nuclei belongs 

 to definite cells, whether sense-, gland-, or urticating-cells ; 

 but the lower one has a part in no specific cells, it belongs to 

 particular elements which are wedged in between sense-, 

 support-, or urticating-fibrils. These cells have no con- 

 nexion with the fibrils adjacent to them, such as we have 

 seen, for example, in the case of the sense-cells ; here they 

 are rather loosely contiguous, and penetrate the fibrillar layer 

 with their processes. Nevertheless we can hardly assume 

 that in them we have to deal with nerve-cells ; they are rather 

 simple embryonal cells, which serve to complete the epithelial 

 layer (figs. 7 and 8, em. z). 



I can scarcely say much about the nerve-layer, nor can I 

 give by any means so detailed a view of it as has been fur- 

 nished for the Actinia by the brothers Hertwig. My state- 

 ments are limited to the demonstration that the structure is 

 the same in both cases. The nerve-layer is shown with par- 

 ticular distinctness in sections, when it appears to be partly 

 finely granular, partly fibrillar; but whether this layer is 

 formed by the basal extremities of various epithelial cells or 

 whether independent fibres take part in it is hardly to be 

 decided. While on the one hand the nerve-layer is connected 

 with the epithelial cells, on the other it gives off fine fibrils to 

 the underlying muscular layer. With a view to parallelization 

 with the Actinia I must state that the nerve-layer is dis- 

 tributed everywhere in Folyparium^ and occurs both in the 

 buccal cones and in the buccal disk, as is described in the 

 case of Gerianthus among the Actiniae. 



The muscular layer follows immediately upon the nerve- 

 layer and consists of long and very thin, smooth fibres, which 

 appear quite homogeneous and bear no nuclei or cells ; as 

 usual, these fibres lie in special depressions of the supporting- 

 lamella^ and are undivided and, as it were, adherent as usual 



