THE CLAVIFORM POLYPES. 35 



developed at the extremity of each, exactly like that at the 

 extremity of the stem, and which follows the same com-se 

 of development. In this way we witness the gradual 

 formation of all the individual cells {a a a a a, fig. 48,) 

 of the first form, on the compound polype which originated 

 in one of the minute ciliated creatures. 



When the cells and polypes of the branches are fully 

 formed, other cells, much larger and difierently shaped, 

 spring up in the angles between the stem and branches 

 (fig. 48 ^ d (5, and magnified fig. 52.) They are formed 

 exactly in the same way as those first described, but are 

 always nearly sessile and provided with an arched opercu- 

 lum, from which the softer annularly expanded, substance 

 does not shrink (fig. 53 ;) consequently the animal does 

 not complete its tentacula, nor protrude itseK from the 

 cell. On the contrary, other and still more interesting 

 phenomena are exhibited ; for new individuals are gene- 

 rated between the outer and inner membranes surround- 

 ing the so-called intestinal tube, upon which are now 

 fonned small elevations (fig. 52 ^,) at which the granules 

 of the interior fluid appear to be detained. These pro- 

 jections increase in size and become rounded, and their 

 connexions with the intestinal tube more slender, though 

 never entirely destroyed. External to these vesicular pro- 

 jections, some perfectly spherical bodies are visible (fig. 52/) 

 of an opaque substance, but presenting a clear round spot 

 like an included vesicle (fig. 52 g) on their external side. 

 The globular bodies, two of which are placed on the exter- 

 nal aspect of each vesicular projection of the central tube, 

 are inclosed in a delicate transparent membrane (fig. 52 h) 

 on the outer side of which is a circlet of minute tubercles 

 (fig. 52 k) During the continued development, which 

 always takes place from above downwards, so that its 

 successive steps may be observed in the series of vesicular 

 elevations ranged one above another, the uppermost trans- 

 parent sac with its contents approaches the operculum of 

 the axillary cell and breaks through it, without, however, 

 losing its connexion with the central tube. The succeeding 



