51 



There is doubtless a close and beautiful analogy between 

 the stages of the development of the Medusae and those of 

 the Tree ; between the larva of the one and the leaf of the 

 other, between the ovum of the animal and the seed of the 

 plant. Yet this comparison does not explain the essential 

 condition of gemmation in either : one thing unexplained 

 cannot be made to illustrate another unknown thing. One 

 seems to get some knowledge when it is stated that the 

 leaf is produced ' by continuous growth, 5 and that the bud 

 of the Hydra is produced like the leaf. And had the re- 

 viewer recognized the essential concordance between the 

 'continuous growth 5 of the conferval filament and that 

 which augments the germinal mass in the ovum, he might 

 have arrived at the desired explanation; but he affirms 

 them to be f altogether distinct/ 



Admitting the obvious analogies between the reproduc- 

 tive phaenomena of the Medusa and the Plant, Dr. Car- 

 penter says, " the whole of these phaenomena appear to us 

 to constitute but a single generation, instead of making 

 two, as represented by Steenstrup;" and, availing himself 

 of the popular idea that a tree is one individual living 

 thing, he turns those analogies with apparently great power 

 against the definitions of Professor Steenstrup. 



It is quite true, as the able reviewer says, es that men 

 are not in the habit of speaking of leaf-buds and the flower- 

 buds of a plant as of two distinct generations." But before 

 the whole doctrine of the ( alternation of generations 5 is 

 knocked to the ground (p. 205), those who desire to secure 

 for the ingenious Danish Professor the credit which he 

 really merits, may bring to his support that other and per- 

 haps truer interpretation of the phaenomena and analogies 

 arrayed against him, to which I have before referred in re- 

 gard to his opinion of the sex of the budding polype. 



The fertilized ovum of the medusa-parent is like the fer- 

 tilized ovum of the Aphis, and the polype that grows from 

 it resembles the first larva into which the embryo Aphis 



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