120 ZOOPHYTES. 



This generation of 1838 having perished at the end of the same sea- 

 son, still a third generation occupied the bark in June 1839. Being now 

 between fifty and sixty miles from its original abode, I could entertain no 

 doubt that the hydra composing it sprung from those of the preceding 

 year. They amounted to hundreds in the first week, all perfectly white ; 

 none had above 36 tentacula at most, nor were they yet divested of their 

 shells. 



This third generation proved to be the identical resemblance of the 

 progeny of the original parent of the stock ; no essential change of struc- 

 ture had taken place, for the evolution of additional tentacula seems inci- 

 dental to age and permanence, probably in proportion to both. 



Even a fourth brood was hatched from the same piece of bark in the 

 first week of June 1840, all the hydrse being white as previously. They 

 did not subsist long ; neither did any appear in the beginning of August, 

 when a few ova, presumed to be recent, were observed. 



In the course of the history of the Sertularise in the preceding volume, 

 numerous illustrations of their mode of propagation by means of ova, or of 

 embryos contained in vesicles, have been given. Nothing of this kind is 

 ascribed to fresh-water zoophytes. Nor ought the observer to yield to de- 

 lusive appearances, to prejudice, or hypothesis, without the strictest scru- 

 tiny. Minute vascular bodies were observed on the surface of the bark 

 above described during the month of May 1838, that is, the year subse- 

 quent to its removal from the pond. In various places six or eight were 

 closely approximated, even in contact, others solitary ; and they were dis- 

 tributed more numerously on the outer than the inner surface of the bark. 

 They stood always irregularly, some of them contained also in vacuities, 

 covered by loose portions of its substance. 



These vesicles are affixed by the smaller extremity ; they are hollow, 

 with a dentate orifice, of dingy white colour, superficially speckled black. 

 Fig. 18. 



It would be vain to speculate on the peculiar nature, or to assign any 

 special province to bodies so minute in such a situation, and subject to 

 scarcely more than general inspection. They might not be animal pro- 

 ducts. 



