Reproduction in the Hydra viridis, 289 



lavish expenditure of her care in providing secure means for the 

 continuance of the species of animals. They call our attention 

 to the remarkable fact of the existence of two distinct kinds of 

 g-enerative elements, even among the simplest of animals. 

 They thus add probability to the view deducible from an ex- 

 tended consideration of the recent observations in the vege- 

 table as well as the animal kingdom, that in no instance is a 

 new organized structure, under the form of an ovum, seed, or 

 spore, separated from a parent, and made capable of producing 

 a new being, without the concurrence of generative elements 

 of two kinds — one of these being itself a cell, or in a vesicu- 

 lar form ; the other being a peculiar product of cell develop- 

 ment, and most frequently assuming the form of minute fila- 

 ments endowed with a power of rapid vibratile motion. Lastly, 

 in contemplating the alternate production of buds and ova from 

 the same situation in these polypes, they suggest the inte- 

 resting speculative inquiry whether the concurrence of a male 

 element is necessary to give fecundity to the germ of a mere 

 bud — a view in regard to which, although some circumstances 

 appear to give a show of probability, the want of sufficient ob- 

 servations forces us in the meantime to suspend our judgment. 



Description of the Plate. 



Figure I. Hermaphrodite individual of the Hydra viridis attached by its foot to a 

 portion of the root of a Lemna ; a, ovigerous capsule ; bb, spermatic capsules, mag- 

 nified ten diameters. 



Figure II. The ovigerous capsule burst, its granular contents fscaping. 



Figure III. The spermatic capsule burst, with some of the spennatic filament* 

 in fasciculi near it. (The two last figures are more highly magnified than the fir-t.) 



On the Glacial Theory, and the Effects of Glacial Action. 

 Communicated by the Author. 



The history of the Glacial Theory affords another example 

 of that apparent fatality which has ever attended the advance- 

 ment of each new discovery in science. The evidence of 

 the former extension of glaciers has now been sufficiently 

 long before the public to enable them to form a correct 



