COMPENDIUM. 291 



which is discharged on maturity, without undergoing farther metamor- 

 phosis than ensues by developement of the parts in evolution of rudimen- 

 tal tentacula from one side, and the origin of a stem from the opposite 

 side. 



This cyst bears the narrowest general resemblance to a matrix, in its 

 long retention of an individual being, gradually nurtured there and brought 

 to maturity. 



These cysts, however, may amount to 500 ; each seems indepen- 

 dent of the rest, though pendulous in clusters like bunches of grapes. 



Whatever be the earlier stages of metamorphosis here, they have 

 taken place before expulsion of their subject from the cyst. 



The vesicle of the Sertularia, so profusely distributed over specimens, 

 is a matrix of another kind, wherein an animal sui generis originates, and 

 is nurtured until expulsion, when it has still to undergo a complete meta- 

 morphosis in progress to perfection. 



Perhaps the nearest approach to a real ovum with an indurated shell, 

 is seen in the ovum of the Cristatella mucedo, together with the ova of the 

 Alcyonella, and the Plumatella, all compound zoophytes, with lunate as- 

 cidian hydrae. In these we observe that the ovum consists of two shells, 

 like watch-glasses, which sunder naturally, as the young gains sufficient 

 strength to quit this its early abode. 



The precise relation between the hydra and the ovum of the Crista- 

 tella, is not explicit ; and it is almost equally obscure in the Alcyonella. 

 Others may have done so, but I could never ascertain that there is a spe- 

 cific ovarium common to the whole specimen, situated in the common 

 substance, the polyparium, basis, or sole ; and whether ova, one or more, 

 be generated in each hydra. They have never occurred in such num- 

 bers as to sanction belief of this latter as the fact. 



None of the hydra; of either the hydraoid or ascidian zoophytes above 

 mentioned, are sensibly endangered from the existence of originating pro- 

 geny. But, with the lunate zoophytes, maturity of the ova is the prelude 

 of decay. 



One mode of perpetuation among the simple and the compound As- 

 cidise demands particular and attentive notice, from its singularity. Al- 



