TUBULARIA. 47 



seen from the preceding detail, that seven hydrse subsisted in 66 days ; 

 that their average duration, including the interval of their absence, scarcely 

 exceeded nine days ; — that a new head might even unfold and occupy the 

 place of one which had been in existence the preceding day. 



The progressive degeneration of external organs, whether in size or 

 number, is no less remarkable, — as if evincing the gradual exhaustion of 

 the resources or energies of nature. Contrasting the fine, florid, and luxu- 

 riant hydra with 22 tentacula, and some remote successor, pale and di- 

 minutive, with only 6 or 7, proves the difference between feeble and vigo- 

 rous evolution. 



In probing the embryonic sources, a subject of such profound interest 

 to the philosopher, arguments might be reared against the infinite evolu- 

 tion of germs, from the nature of the reproductions of the two species of 

 Tubularia now described. Some might certainly maintain that were such 

 the primitive order, all the germs would unfold the true complement of 

 organs, distinguishing its peculiar kind, though of diminished size. But 

 if the germ be generated immediately in the parent, it might be said that 

 the production of animals in such rapid succession impairs the quantum of 

 elementary matter to be derived for each, which shall suffice for the 

 nucleus of the offspring, — whence the organization of the successive hydrae 

 degenerates Likewise, some may conclude that the primitive or succes- 

 sive germs are not all reposited in a magazine of vitality, seated amidst 

 the pith or elsewhere deep in the stem, but that the embryo may be gene- 

 rated from the internal surface of the fistulous tube below, or foi-med in 

 some invisible cell, by the organic energies of the parent. 



If we admit the universal vascular structure of the elementary parts 

 of animal matter, the theory of primitive germs is supported, because the 

 dilatability and increment of the parts, resulting from the institution of 

 life and consequent nutrition, may adapt them for the benefit of the per- 

 fect being. 



Perhaps there are varieties of this and the subject of the next chap- 

 ter, which perplex the observer in determining on rejecting identity. The 

 want of absolute uniformity which pervades all animated objects, and of 

 which we become sensible as we are more or less acquainted with them, can- 



