Dr. A. Korotneff on Polyparium ambulans. 207 



derm, and a gelatinous intermediate layer are to be found 

 here ; but with them we have two different formations — one 

 in the structure of the whole of the upper wall, the other in 

 the acetabulum. We commence our descriptian with the 

 upper wall, and have here to distinguish two different parts, 

 namely the small buccal cones and the upper surface (between 

 the buccal cones), which we will indicate as the buccal disk. 

 These two parts only differ by the degree of development of 

 their layers ; thus in the buccal cones the muscular layer is 

 quite inconsiderably developed, but between them it is very 

 considerable. In order to understand the structure more 

 clearly we will study a section of the upper wall. This sec- 

 tion is taken parallel to the long axis and perpendicular to 

 tlie septa. 



The ectoderm (figs. 4, 5) is divisible into three separate 

 layers ; the outer one, which at the same time is the most con- 

 siderable, is composed of very long, fine, perfectly filiform, 

 epithelial elements ; the nuclei in this are distributed in two 

 aggregations, of which the upper one is situated close to the 

 nematocysts and the lower one much deeper, occupying exactly 

 the middle of the height {em. z). As the foundation of this 

 outer layer there is a thin stratum of a finely fibrillar substance 

 {Nv) in which a few nuclei are scattered. Lastly, quite at 

 the bottom we find a layer of muscular fibres ( Qm) ; in trans- 

 verse section this appears as an aggregation of shining cor- 

 puscles. The three layers above mentioned are to be regarded, 

 as in the Actinite, as epithelial, nervous and muscular layers. 



The oiiter, epithelial layer contains quite different elements 

 — there are here support-, sense-, urticating-, and finally 

 gland-cells. From the extraordinary fineness of the elements 

 and the involution of the filiform prolongations of their inner 

 parts it is difficult to distinguish the support-cells from the 

 sense-cells, and I have only succeeded in seeing clearly the 

 sense-cells. These are elements drawn out into a thread-like 

 form [sz], of which tlie nuclei are situated in the first third 

 of the cell and in the section form the aggregation which is 

 closely approximated to the lower extremities of the nemato- 

 cysts. The protoplasm accumulates more strongly in the 

 neighbourhood of the nucleus, and hence there is a thickening 

 of the sense-cell which is produced inwards towards the 

 periphery into a fine process ; the process, however, appears 

 not to be plasmatic, but fibrillar, and even homogeneous. 

 From the single specimen of Polyparium at my disposal, and 

 which was hardened in alcohol, I rarely succeeded in obtaining 

 good teased-out preparations ; nevertheless I was able to 

 convince myself that here matters are exactly as in the 



