36 DEVELOPMENT OE 



sacs then follow the same course, until the whole series 

 is exhausted, in consequence of which, the polype of the 

 axillary cell seems to shrink ; but it is constantly again 

 covered with a flat operculum or membrane, which adheres 

 to the border of the cell, and surrounds the slender con- 

 nexions of the sacculi with the central tube. Meanwhile 

 the apparent saccuh open (fig. 53 /5); and a circlet of about 

 twelve irregularly-toothed tentacula projects around the 

 opening, and it is now seen that the sacculi are in fact 

 globular individuals, in which four longitudinal vessels 

 proceeding from the base of the tentacula to the bottom 

 of the body, represent the four vessels met with in the 

 more fuUy-developed coryn(B. 



Thus these globular individuals are completely developed 

 females, and the opaque globules contained in them, ova, 

 in which the clear spot is the germinal vesicle [vesicula 

 Purkinji.) When the embryo is fully developed, it rup- 

 tures the dehcate membrane of the egg and escapes, 

 remains for some time within the parent animal, through 

 whose opening, however, it afterwards passes into the 

 water, attaches itself to a fixed object, and becomes the 

 origin of a new compound polype, in which the same 

 process of development is repeated. The parent animal 

 dies off or withers, having fulfilled its function. 



Upon reviewing this sketch, it can hardly be considered 

 to present an instance of metamorphosis, since it is not 

 the same individuals which in the course of time exhibit 

 various forms, but we see here also, a series of genera- 

 tions whose succession in a definite order is necessary to 

 the complete development of the species. The ciliated 

 embryos which, by their adhesion lay the foundation of 

 the polypes, originate only from ova, which are developed 

 in the females. These latter are generated between the 

 inner and outer tunic of the polype in the axillary cells, 

 which polypes may consequently be considered as the 

 " nurses" or foster-parents of the female individuals, 

 whilst they are themselves, on the contrary, derived from 

 a previous generation of polypes of a different form, 



