96 ZOOPHYTES. 



protrude, with the lapse of the following week ; yet the mass still shifted 

 its place ; and in twenty-eight days from the date of manifesting the utmost 

 vigour, now completing the fourth week, it was reduced to the shape and 

 dimensions shewn by fig. 3. Entire decay of this interesting subject 

 ensued in another fortnight. 



Meantime, the ova, generally resting on edge, become greatly com- 

 pressed by the shrinking flesh, and are brought more and more to this 

 particular position, which probably facilitates their escape through the now 

 attenuated substance of the Cristatella. 



No hydra? were displayed by the preceding specimen after the 4th of 

 October. The ova continued escaping, some singly, some in clusters of 

 three or of six : the whole amounted to twenty-five ; some of them con- 

 nected with, or invested by, gelatinous matter. 



I know not whether the foregoing observations on this particular 

 race of zoophytes, or on a few yet to follow, remount high enough to 

 reach the formation of the embryo in the ovum. The earliest stages of 

 the ovum itself are concealed from our view by its position. It may be 

 questioned whether, at the moment of its escape from the parent, the 

 development of the rudiments of the embryo has commenced. But this 

 will not affect the fact that zoophytes do actually produce inert bodies, as 

 the ova of birds and other animals, wherein the elements of the progeny 

 are nurtured and come to maturity. 



The ovum of the Cristatella has a hard shell, with yellowish fluid 

 contents. The»planula from the Sertularia, the gemmule of the Flustra 

 and Alcyonium, and the spinula of the Botryllus, are all endowed with 

 vigorous activity, when discharged from each of the parents, which them- 

 selves are immoveably rooted. But, the ova from the Cristatella, which 

 itself is free, are void of the faculty of motion. 



The shell of the ovum may be compared to two meniscus valves, that 

 is, it much resembles two watch-glasses united by the edges. 



In 202 days from its escape, the edges of the ovum begin to gape, 

 like the separating shells of the bivalve Tcstacea, gradually widening to 

 allow protrusion of the nascent Cristatella, as the halves shall sunder 

 more.— Plate XXVII. fig. 5. 



