56 Prof. Reichert on the Contractile Substance and 



traction also sometimes appear very regularly distributed, and 

 thus cause the polyhedric epithelial marking, as the nuclei of 

 which scattered and covered urticating organs have been 

 indicated. 



8. The papilliform processes may become elongated into 

 actual root like feet, which, in most cases, are employed for the 

 attachment of the body. In Hydra such root-like feet have been 

 observed on the margin of the pedal disk ; in the Campanularice 

 and SertularicB they rather occur isolated on the stem, but more 

 frequently and often in larger numbers on the ''^ transition - 

 piece/^ The root-like feet here adhere by means of a disciform 

 dilatation to the polyparium, and have been more or less di- 

 stinctly indicated as supposed stable bands in the figures of pre- 

 vious authors. In the Hydrid(2 such root-like feet of filamentous 

 form are developed in greater number also on the inner surface 

 of the contractile layer, and attach themselves firmly to the sup- 

 porting lamella. These are the muscular fibres of the HydridcB 

 mentioned by Kolliker. Filiform pseudopodia with the so-called 

 granular movement were not observed. 



9. The second principal constituent of the body-wall, the 

 endoderm, consists throughout of a simple layer of cells, which 

 is for the most part spread out like an epithelium and provided 

 with cilia. The form of the cells varies according to the state 

 of contraction of the true contractile layer. In the extended 

 state the cells are rather flattened, and in Hydra even frequently 

 drawn out in the direction of the longitudinal axis ; in propor- 

 tion as abbreviation takes place their thickness increases, and 

 the cellular layer finally acquires the aspect of a cylinder-epithe- 

 lium. It is not demonstrated, even in Hydra, that these cells 

 can change their form by their own contraction ; indeed this is 

 even highly improbable. The inner surface of this cellular layer 

 is turned quite freely towards the cavity, which is filled with nu- 

 tritive fluid containing granules. Any pigment-granules that 

 may be present are situated within the cells, and never form a 

 separate layer (Agassiz). 



10. The supporting lamella consists of a limpid, textureless, 

 soft, elastic substance, which, at ordinary temperatures, only 

 swells up a little in solution of potash, or even in chemically 

 pure sulphuric acid, and does not dissolve even when treated 

 for half an hour with the above-mentioned reagents. The sup- 

 porting lamella must be regarded as an excretion of the con- 

 tractile substance, as, in Hydra, it occurs even in the free ter- 

 minal portions of the tentacles, where the inner cellular layer is 

 deficient. Consequently the contractile layer, both on its outer 

 and inner surfaces, forms excretions which gradually become 

 solid, for its own protection and support. In the Campanularia 

 and SertularicB the external excretion forms the polyparium, and 



