168 ZOOPHYTES. 



there is no regular difflision. The spine rises from a socket, with an ir- 

 regular extremity, fig. 25 ; and it advances so as to bear hydrse, by simple 

 prolongation, without diffusion, securing it below. — Fig. 26. 



All these facts have been illustrated by a variety of observations made 

 throughout the course of many years, and at different seasons of the year. 



No essential distinctions farther than might be expected from the 

 mutable form of soft-bodied animals, are seen among the planulae. 



A specimen with green hump or gibbous vesicles, such as PI. XXX. 

 fig. 1, produces green planulae, figs. 2, 3. In all, where the regular pro- 

 cess ensues, the root breaks into divisions, fig. 4 ; with originating stalks 

 and nascent hydrse, figs. 5, 6. Some of these products are less regular, 

 though all with pith, occupying a wide sheath, fig. 7, as previously ex- 

 plained. 



But the observer is very liable to be deluded by peculiarities, the same 

 specimen exhibiting hydrae from an orifice scarcely elevated above the 

 branch which bears twigs with frills and hydrae, quite distinct and separate 

 from them. There is also a most conspicuous difference in the form of the 

 vesicle ; for some green specimens bear both ovoidal and gibbous vesicles ; 

 and grey specimens or green specimens bear both ovoidal vesicles, and 

 such as are of a very different character, as in Plate XXIX. fig. 6, already 

 adverted to. While the green vesicles produce green planulae, fig. 11, the 

 grey vesicles produce grey planulae, fig. 27. A few specimens bear a long 

 green prunate or plum-shaped vesicle, which I have never seen in such 

 maturity as to afford any produce. — Plate XXX. fig. 12. 



The principal external difference sensible in complete adults is in 

 some bearing green vesicles, as that of Plate XXVII. on the larger parts, 

 and white or very light grey vesicles on the slender white parts, and in some 

 bearing yellow vesicles exclusively, as that of Plate XXVIII. fig. 1. This 

 latter was a fine and prolific specimen, the hydra pale green. The vesicles 

 were in hundreds. Beautiful yellow planulae issued from them about the 

 middle of May, in such numbers, that, rising on the side of the vessel, their 

 accumulation formed a yellow ring just under the surface of the water, 

 fig. 2. A multitude of Sertulariae sprung from them, the furthest advanced 

 of which had thre6 hydrae and a bud on May 26. 



