Structure of the Campanularise, Sertularise, and Hydridse. 57 



the internal one the supporting lamella ; in the Hydrida the 

 supporting lamella alone is formed; in other cases {Gromia &c.) 

 only an outer skeleton makes its appearance. 



11. The tentacles of the Hydrida are simple tubes, the cavity 

 of which is in open communication with that of the stomach ; the 

 granular nutritive fluid moves through the tentacles as well as 

 through the cavities of the head and foot. From the morpholo- 

 gical nature of the wall of the tube, two divisions must be distin- 

 guished in its length, namely, the attached and the free terminal 

 division. On the former the wall is composed of the same con- 

 stituents as on the head and, especially, on the foot ; in the free 

 division the inner, cellular layer is wanting. In the tentacles of 

 the Campanularice and Sertularia the inner, cellular layer is also 

 wanting, and, indeed, throughout their whole length. But from 

 the supporting lamella septa are given off at regular intervals, 

 dividing the cavity of the tentacles into chambers, which pro- 

 bably communicate with each other by a central orifice in the 

 septum. In the fully developed state of the animal these cham- 

 bers contain no cells, neither cartilage nor epithelial cells. In 

 each chamber the contractile axial substance described by me is 

 situated; this is of exactly the same nature as the external con- 

 tractile layer, only wanting the urticating organs. In the ab- 

 breviated state the contractile axial substance fills each chamber 

 almost completely; in a more or less extended state the cham- 

 bers are filled from the stomachal cavity with a fluid which 

 never contains granules, and appears to be clear sea-water. The 

 contractile axial substance then occupies the axis of each cham- 

 ber, extending from one septum to the other : its form differs 

 according to the state of contraction; on the septa it spreads 

 out like a disk, perhaps by means of processes ; it often pre- 

 sents the form of a ramified cell. Like the outer, contractile 

 layer, this axial substance presents no trace of a cell-nucleus. 

 Knot-like inflations, or urticating organs, placed in front or 

 behind in the outers contractile layer, may produce the illusive 

 appearance of a cell-nucleus. 



12. The movement of the nutritive fluid takes place quite in- 

 dependently of any cilia that may be present on the inner, cel- 

 lular layer, merely by the agency of the contractions of the outer, 

 contractile layer. 



13. The comparison of the hollow body of the Hydrozoa to 

 the first traces or stages of development of the organism of the 

 higher Vertebra ta undertaken by Huxley and afterwards by 

 Kolliker, has no foundation in fact ; it even proceeds from er- 

 roneous suppositions, both as to the nature and signification of 

 the first foundation of the vertebrate animal, and with regard to 

 the structure of the body of the Hydrozoon. 



14. As both the outer skeleton {pobjparium) and the inner 



