ZOOPHYTA HYDROIDA. 87 



tents. * The number of the gemmules in each vesicle, and 

 their shape, varies in every species. In the vesicle they are 

 connected to a central placentular column, though there are some 

 exceptions to this, and when mature they escape outwards by a 

 disruption or fall of the lid which closes the top, being extruded 

 in succession and, in some cases at least, after intervals of some 

 hours. It appears to be deducible from some figures of Ellis, f 

 rather than from his expressions, X which are equivocal, that the 

 ovules are sometimes developed into perfect polypi before their 

 expulsion from the matrix, but the fact, though not incredible, 

 needs confirmation, and it is certain that their birth in the ovi^ 

 form condition is the general rule. At this period they are 

 clothed with cilia, as Ellis has figured them, § and as Professor 

 Grant first distinctly brought into view ; and by means of the 

 rapid vibrations of these minute organs they are carried to 

 and fro through the water for some time, varying from a 

 few hours to two or three days, until, having at length in due 

 course settled on a proper site, they throw out, in the man- 

 ner of a vegetable seed, a root-like fibre to fix themselves, 

 and then push up a shoot as a commencement to the fu- 

 ture polypidom. || Polype-cells and polypes are rapidly evolv- 

 ed on the sides of this shoot, and nourishment being now re- 



* So that Hedwig's axiom, adopted by M. Virey, " that the reproductive 

 organs of animals are contijiuous with the life of the individual, while the repro- 

 ductive organs of perennial plants, when their functions have been performed, 

 are thrown off, and replaced hi the succeeding season by others,"— must be re- 

 ceived with some limitations — See Tiedemann's Comp. Physiology, p. 7G. 



t Corall. pi. V. lig. A. t Corall. Introd. p. x. 



§ Corall. pi. xxxviii. fig. B. 



II Mr Lister has minutely described the ova of Campanularia gelatinosa. 

 " The ova were roundish, and consisted of two portions ; the outer and more 

 transparent, that might be called the white, inclosing an inner bag filled with 

 particles in fluid like those in the currents of the stem, and connected with 

 them by the cord. The current and agitation were seen in the inner bags only, 

 and the flow into and from them alternately along the cord was strongly marked." 

 As they approach maturity " the ova became more opaque, which hid the 

 changes that might be taking place within them. The number in a full ovai-y 

 was about seven." When mature they emerged from the cell " in succession 

 at an average interval of six hours. The protrusion took about a quarter of an 

 hour, and was connnonly preceded by a transparent projection, like torn mem- 

 brane, before the end of the ovary, and a few active particles in tlie water." 

 —Phil. Trans. 1834, n. o75. 



