7 



The mode of growth and the nature of the sheaths or horny 

 envelopes, have been matters of curious speculation ; and 

 to the present time are by no means settled points. When 

 a seed or gemmule has become fixed, in the manner described 

 above, and the roots thrown out from the base; the central 

 pulp and its horny envelope become elongated superiorly. 

 Taking the Laomedea geniculata, as an example, the central 

 pulp of the gemmule becomes the pith; and after it has been 

 elongated for a short distance, a lateral enlargement or rather 

 elongation, takes place in the central pith, with a corres- 

 pondent enlargement of the horny investment ; this increases 

 in length till it has become as long as the usual pedicle of 

 the cell; at its termination it then becomes enlarged and 

 bulbous, and the pedicle acquires a shrivelled appearance, 

 which proves afterwards to mark the rudiments of the rings of 

 the cell stalks. In a very short time the bulbous termination 

 acquires a deeper tint towards its centre, and becomes lighter 

 towards the circumference. At first the central shade is 

 slight and indistinct, but soon becomes darker and more 

 defined. As this condensation or organization goes on the 

 pulp gets much more transparent towards its circumference, is 

 drawn towards the central condensation and leaves behind it 

 a transparent horny covering; and during this stage, it is very 

 common to observe the semitransparent circumference of the 

 pulp drawn into transverse folds, as if they were produced 

 by a force acting towards the centre. In this way the pulp 

 of the future polype is separated from the sheath. This 

 being effected, the pulp acquires a serrated edge superiorly, 

 and gets contracted inferiorly into the shape of the perfect 

 polype. The serrations on the superior surface advance, 

 and the tentacula are elaborated from them and folded on 

 each other. Up to this point the cell is closed, and the 

 polype excluded from any contact with the water. The 

 superior portion of the horny sheath now gets thin, but not 

 from pressure, as the polype is not in contact with it; and 

 finally gives way about its centre and falls in, so as to give 

 the cavity a funnel-shaped opening. The polype now feels 

 the influence of the surrounding water, and immediately 

 springs into active life, using its tentacula and capturing its prey 

 as readily as the older ones. The funnel-shaped opening to the 

 cell soon disappears and the differences which constitute the 

 specific characters are formed. The stem is elongated in a 

 similar manner ; the pulp advances at one time the length of 

 the articulations and stops for a short time, in the smaller 

 kinds, till the cells and polypes are somewhat perfected ; but 

 in the larger and more luxuriant species this can hardly be 

 distinctly noted, as the growth of several inches sometimes 

 takes place in a very limited time. In the S. polyzonias, 



