210 Dr. A. Korotneff ow Polyparium ambulans. 



which is to be observed in the Actiniae, will be sufficiently 

 clear to us. The first step is that in which the cnicloblast is 

 closely applied to the fibril, forms its essential muscle-cell, 

 and therefore, together with the fibril, cannot be characterized 

 otherwise than as a true muscle-form. However, we shall 

 find that the cnidoblast itself is by no means to be regarded 

 as an integral part of the muscular fibre, because it remains 

 at some distance from the fibril itself (tentacles of Physophora) 

 and communicates with the fibril by means of fine filaments. 

 If this notion needs any further confirmation we must pay 

 special attention to the connexion between the cnidoblast and 

 a muscular fibril in Polyparium ambulans ; in my opinion it 

 proves incontrovertibly that the cnidoblast in Polyparium is 

 a true muscle-cell which, in the metamorphosis of the ecto- 

 derm, has entirely quitted its original situation and taken up 

 a peripheral position (fig. 8) . In this way we shall recog- 

 nize that the same course of transformations of the muscle-cell 

 exists for all the other elements of the Actinian body ; nerve- 

 cells, sense-cells, gland-cells, and cnidoblasts are therefore to 

 be regarded as metamorphosed epithelial muscles, and hence 

 we may assume that the first step in the metamorphosis of an 

 embryonal cell is the separation of a muscular fibril j but 

 herewith the cell does not appear to have exhausted its 

 powers of furnishing something else, and thus are produced 

 the histological double-structures already more than once 

 described (by the brothers Hertwig in the Actiniee and by 

 myself in Hydra and the Siphonophora) , such as epithelial 

 muscle-cells, nerve-muscle-cells *, sense-muscle-cells, and 

 gland-muscle-cells. As a matter of course this histological 

 process appears to be the longer one, and may be often greatly 

 abridged, and an embryonal cell, without satisfying the 

 first requirement of the organism, the need of locomotion, 

 directly acquires various specific properties, and becomes 

 converted directly into a nerve-, sense-, or gland-cell, over- 

 leaping the intermediate stage of the myoblast. 



The supporting lamella is an elastic membranule (figs. 4, 

 5, St. /), which is considerably thicker in the lateral margin 

 than in the upper surface of Polyparium and much thicker 

 than in the buccal cones. Throughout it consists of fine felt- 

 like fibres which are imbedded in a homogeneous intermediate 

 substance. Between the fibres there are numerous small 



* Especially since the discovery of special nerve-cells in the Hydroida 

 I cannot recognize the epithelial-muscle cells in Hydra as true neuro- 

 muscle cells in Kleiuenberg's sense. Nevertheless the ingenious neuro- 

 muscle theory remains still vaUd. 



