154 ZOOPHYTES. 



with two buds protruded from each of other two globules still suspended. 

 The evolution of their hydrse ensued on May 21, when favourable micro- 

 scopical observations ascertained, that the animals, of a grey colour, were 

 each provided with about 25 deeply muricate, almost moniliform tentacula. 

 They were of lively nature, enjoying the element, and seeking a safe re- 

 treat in their cells. It was easy to identify them with the hydrse of the 

 adult product, which had borne the vesicles. 



At this early stage, the real structure of the Sertularia afterwards 

 disguised by supervening opacity, is admirably exposed : And here is 

 shown, in an especial manner, the great advantage of examining living 

 beings under every aspect. The stalk issues visibly through an aperture 

 in the summit of the spherule. Its dark yellow pith is clearly followed 

 upwards through the transparent tubular stem, until dilating above into 

 the young hydrse, while the extremity of the tube itself is enlarged into 

 cells, sufficiently capacious for their tenants. — Fig. 15. The spherule yet 

 rests on its pedestal, though here intercepted from view. 



The cells are generated simply by prolongation of the tube, and they 

 stand in alternate arrangement, diverging to right and left in the same 

 plane. But this prolongation is dependent on the vigour of the pith, for 

 its presence is the indication of vitality. The evolution of the hydrse, in 

 relation to each other, is successive. Thus the lowest flourishes first, and 

 next that above it. As the cell seems derived entirely from the tube, so 

 does the hydra seem to originate exclusively from the pith. The cell, once 

 formed, does not depend on the subsisting of the hydra, at least in this 

 species of zoophytes, but in some of the campanulate (Sertularian) zoo- 

 phytes, the cell is not permanent. 



The prolongation of the stem of the Sertularia abietina, is always in 

 proportion to the successive generation of cells. One bearing only two, 

 is of about equal length to three cells and a half Deviations from regu- 

 lar arrangement frequently occur among nascent Sertularise. 



Many young specimens had now two hydrse, with their cells, on 

 May 24. An embryo, still immature, darkens a third cell, during the 

 growth of this Sertularia, fig. 16. One had three hydrse, May 25, which con- 

 tinued in beautiful display until June 27, fig. 17 ; only a single specimen ac- 



