COMPENDIUM. 29a 



but each subsequently occupied by an embryo hydra, which gains maturity 

 as the cell is perfected. Several rows may be in progress at once. 



Now, the first row thus newly generated, is thin and transparent, the 

 sides of the cells indistinctly defined, while the centre is vacant. A second 

 marginal row is generated from the first ; and a third from the second, all 

 proceeding outwards, and which, in their early origin, are precisely as here 

 described. As these are advancing, a fourth perhaps appears, which is at 

 that time the outermost, and alike transparent and empty. 



The bydrse of the old marginal row may be still vigorous, or they may 

 have disappeared by decay. The hydra? of the first new row adjoining it 

 are yet only in embryo, while the cells of the fourth new row, daily becom- 

 ing more conspicuous, are still empty : no rudiments of the future tenants 

 are visible. 



Shall it be concluded that the fourth, or external new row, is derived 

 from either the first, the second, or the third ? 



The question here involved depends on similar principles, involving 

 the source of increment, augmenting the Flustra hispida and others. 



It is one of much interest. 



The propagation of zoophytes is not so rigidly limited to certain sea- 

 sons of the year as that of a multitude of other animals, terrestrial and 

 aquatic. It advances apparently, at most times, vigorously and uninter- 

 ruptedly. 



But the lower tribes are not susceptible of organic evolution during 

 the prevalence of rigorous cold. For this peculiar process, a certain tem- 

 perature is always indispensable. The waters, however, are less readily 

 affected than the air by refrigeration : And, in fact, I have observed the 

 rate of multiplication during winter almost equivalent to what it is in 

 zoophytes during spring or summer. 



Nevertheless, Nature seems, by one of her paramount ordinances, to 

 have appointed the more evident preparations for preserving the continu- 

 ance of the animal and vegetable world, during March, April, and May, 

 which is the principal season of the multiplication of zoophytes. 



Possibly, in respect to the terrestrial tribes, it is that the young may 

 be strengthened by approaching summer. 



