120 ZOOPHYTES. 



In some they were shorter and less regular. Indeed, if we reflect on their 

 original office of seizing or conveying food to the mouth, their functions 

 are now no longer necessary. Apparently the base of the pillar rests on 

 the wonted site of the mouth of the hydra. 



But in the next place, before the progress of the subjects composing 

 the roll is very far advanced, the circular row of tentacula at its extremity 

 disappears. It is entirely obliterated. — PI. XIX. fig. 6. Now a new row 

 is discovered, — sometimes emerging as simple stumps or protuberances, — 

 from the circumference of the fleshy bulb whereon the root or base of the 

 pillar is implanted, therefore, not in the vicinity of the first or terminal 

 row. They are removed by a considerable interval. — PI. XIX. fig. 6, a ; 

 fig. 7, a. PI. XX. fig. 3, a, c ; fig. 15, a, c. Their growth is more or less 

 rapid. Sensible elongation ensues in 24 hours. 



Meantime the cylinder is extended, the wavings seen on its surface 

 next opening, like basket-work, allow the transmission of light through 

 their interstices; the cylindrical form gradually alters, and the whole 

 figure becomes an inverted conic frustum, enlarging outwards. The bulb 

 also is refining into the shape of a hydra, on the disc of which the summit 

 of the frustum is implanted. — PI. XIX. fig. 8. The same, 24 hours later, 

 is represented fig 9. The subject seems divided into several different 

 strata, or if considered a rouleau, of several distinct coins. 



As the subject apppoaches this stage, a convulsive motion is visible 

 near the extremity, b, figs. 8, 9, comprehending three strata, perhaps, while 

 below and nearer the new circle of tentacula, c, all is tranquil and quies- 

 cent. As the waves have been moulded into cloven lobes, this convulsive 

 motion is occasioned by their clasping inwards, towards the central projec- 

 tion, h, d, fig. 9. Some animal evidently struggles for liberation, which, 

 by vehement and incessant exertion, as said before, at length succeeds, and 

 it swims at large as the Medusa. — PI. XVIII. fig. 1 ; XX. fig. 1. 



Such in abstract was the course of alteration of the subjects investing 

 the shell of the Pecten ; interspersed with which were numerous perfect 

 and symmetrical hydrse. 



First, a smooth fleshy bulb sustained a cylinder of about half its own 

 diameter, indented by plain circles, which were soon converted to waving 



