21 



have been able to observe it, appears as a minute tubercle pro- 

 jecting from the external walls of the cell, and filled with a 

 granular parenchyma. "We next find it hollowed out into a 

 cavity which communicates with the interior of the parent cell. 

 The tubercle, with its cavity, increases in size, and the gemma 

 is now found to consist of an external envelope continuous with 

 the external tunic of the parent cell, and of a thick fleshy 

 lining continuous with the internal tunic. This lining has nu- 

 merous, large, round, nucleated cells distributed through its 

 substance, and internally it presents a rough, uneven surface. 

 The two tunics of the gemma are to become the external and 

 internal tunics of the future cell. 



" By this time the gemma has become considerably elon- 

 gated, and has acquired a clavate form, and its cavity begins 

 to be cut off from that of the parent cell, by the formation of 

 a septum. We next perceive that a rounded mass has formed 

 in the substance of the lining tunic, near the wide extremity of 

 the gemma, and projects into the interior of the latter. In this 

 mass we soon perceive a cavity surrounded by a slightly waved 

 oval ring, which is afterwards to become the tentacular crown 

 of the adult. The ring is at first quite simple, resembling a 

 mere fold of thickish membrane, but in a short time it pre- 

 sents all round a series of minute tubercles, the rudiments of 

 the future tentacula. Delicate fibres may now be distinctly 

 seen passing from the little mass, in which these appearances 

 have been presenting themselves, to the walls of the cavity of 

 the gemma ; these fibres are the rudimental retractors of the 

 alimentary canal. Circular fibres may also be now seen in the 

 lining membrane of the gemma; these are chiefly collected 

 near its proximal end, and are to become the parietal muscles 

 of the adult. The tentacular sheath also may now be per- 

 ceived extending from the base of the rudimental tentacula to 

 the walls of the cavity in which the young polypide is sus- 

 pended, and fibres which are to become the superior parieto- 



