Chap. VII. CLYTIA POTERIUM. 303 



and the changes in the cellular constituents, are essentially the same as in other 

 Campanularians ; but there are some features which are peculiar to this type, in 

 regard to the formation of the calycle. At first the calycle is a thick-walled, 

 pear-shaped, terminal expansion (PI. XXVIII. Fig. 4, c) of the horny tube, and is 

 completely filled by the hydra. As the hydra increases in size, the wall of the 

 calyx thickens most rapidly at a point not far above the base, and projects 

 inwardly {Fig. 6, c) so as to seem to constrict the hj^dra. Next, Ave find this 

 thickening prolonged sharply toward the axis of the calycle, in the form of an 

 acute, triangular-edged, semi-partition {Fig. 6, c), which still further constricts the 

 base of the hydra, and forms a more or less globular space below it, while above, 

 toward the actinal end, the wall very rapidly decreases to a moderate thickness. 

 There is some variation in the degree of progress of the development of this 

 semi-partition (e), for we find, at much older periods {Figs. 7 and 8) than the last 

 {Fig. 6), that the edge is not so sharp, nor prominent, although, as a whole, it is 

 much thicker. Still later, again, we observe that the edge of the semi-partition 

 {Fig. 9, c) is quite as sharp as in Fig. 6, c, but the space below it is compara- 

 tively more extended, and perfectly globular. From the fact, that in a hydra 

 which has reached four fifths of its normal size {Fig. 9) the walls are retracted 

 from a larger proportion of the calycle, and yet the thickness of the latter is far 

 inferior to that of the adult, we infer that, notwithstanding this separation, the 

 hydra has the power to renew, at will, the secreting process, in order to bring 

 the walls of the calycle up to the required thickness. Even at the period when 

 the hydra, being fully developed, pushes ^ the convex cap {Fig. 10, d) of the 

 calyx, and emerges from its hitherto embryonic state, we frequently find the semi- 

 partition apparently no more highly developed than in some of the much younger 

 stages; but this is merely owing to the fact that it does not project at so sharp 

 an angle from the sides of the calyx as it does in other individuals. The cap of 

 the calycle which is pushed off, as the hydra protrudes for the first time, has the 

 form of a watch-glass, whose edge is attached to the margin of the calyx at the 

 point where the wall suddenly comes to a thin, revolute border. 



We may here mention, also, a curious monstrosity, produced by an injury and 

 the consecutive regeneration of a sterile hydra. PI. XXIX. Fig. 1, represents a 

 single hydra which possesses two calycles {a «'), the inferior one of which forms the 

 basis from which the pedicel of the upper arises. It would seem that the termina- 

 tion of the pedicel of the inferior calycle, having lost the head of its hydra, instead 

 of directly budding a new head, first proceeded to grow onward, as a pedicel, and 

 at the same time secreted a horny sheath («'), which was made continuous with 

 the diaphragm {a) at the base of the old calycle, and, of course, concentric to the 

 same; so that there is the curious anomaly of a calycle whose diaphragm is 



