MEMOIR OF SIR J. G. DAL YELL. xli 



he put forth from time to time, phraseology which by no means conveyed 

 his whole meaning. And it is further evident to us, that his observations 

 have been far more prolonged, and have attained on many points a far 

 greater degree of exactitude and completeness, than those of either of the 

 authors we have just named ; and we shall show that one point of funda- 

 mental importance has been clearly estabhshed by Sir J. G. Dalyell, al- 

 though neither Sars nor Siebold was able to make it out ; and that he has 

 thereby been led to a much more accurate conception of the whole pro- 

 cess, than they or their followers have attained." . 



The reviewer then refers to the series of observations by which Sir 

 John proved that the Hi/dra tuba springs from Alednscp, and that the 

 Medusa are themselves the progeny of the Hydra. The process by which 

 the latter breaks up into discs, and becomes separated into independent 

 animals, is minutely described by Sir John : and the reviewer considers 

 the fiict that, while the topmost disc loses its circle of tentacula, a new 

 circle is developed upon the summit of the bulb that remains at the pile 

 of discs, a discovery of great importance, and one which has escaped the 

 notice of other observers. By this means, he says, " the original polypoid 

 body still remains, and may return to its polype life and gemmiparous pro- 

 duction, becoming the progenitor of a new colony of hydraj, every one 

 of which may develop in its turn a pile of medusa-discs. Now, this fact, 

 our knowledge of which is entirely due to the persevering researches of 

 Sir J. G. Dalyell, is of fundamental importiince in our philosophical in- 

 terpretation of this wonderful process." 



A third essay, entitled " Singular Mode of Propagation among the 

 Lower Animals," also appeared in the Philosophicnl Journal in 1835. An 

 essay " On the Eegeneration of Lost Organs, discharging the Functions of 

 the Head and Viscera, in the Holothuria and Amphitrite, two Marine 

 Animals," was embodied in the Report of the British Association, 1840. 

 Another, on " The Reproduction of the Virgularia," appeared in the New 

 Pliilosophical Journal, volume 27 ; and a paper entitled " Examples of 

 Exuviation, or change of the Integuments of Animals," was read at the 

 meeting of the British Association, August 1850, and embodied in their 

 annual Report, 1851. 



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