70 ON THE STINGING ORGANS OF MEDUSA. 



of soil. I hope some of our associates will do so, and let us know the 

 result. 



After having detailed his observations, to which I have referred, 

 Ehrenberg adds that the extraordinary fertility produced by the mud 

 deposited on the arable lands by the overflowing of the Nile, and of 

 some other rivers, probably proceeds, not merely from the mechanical 

 transport of soil, but from the vast mass of animal matters (the inhabit- 

 ants of these minute shells) thus spread over the surface of the land. 



The deposits of the river Dodder to a certain extent corroborate this 

 view, as I know that the stuff spread over the adjoining lands, when- 

 ever it overflows its banks, produces an effect very far from fertilizing. 



The notice which our friend Mr. Ball lately gave of the variety of 

 organic forms which he observed in a morsel of mud from Plymouth 

 Sound, bears on this point, as the rivers falling into that Sound, the 

 Plym, the Tamar, the Tavy, and some others, all flow slowly and for a 

 considerable distance through rich alluvial districts. It would also be 

 interesting to examine the deposits of the Severn, the Dee, the Mersey, 

 and as many other rivers as possible. 



The subject is, possibly, not devoid of economic interest. Irrigation 

 has frequently been resorted to for the improvement of land, but with 

 very different results. It may be that in this discovery of Ehrenberg 

 is to be found the explanation of these differences ; and it is probably 

 not too much to say, that an a priori examination of the mud of every 

 river might enable the agriculturist to say whether he would derive 

 benefit or the reverse by suffering its waters to overflow his ground. 



XIII. ON THE SUPPOSED STINGING ORGANS OF MEDUSA, AND THE 



OCCURRENCE OF PECULIAR STRUCTURES IN INVERTEBRATE ANIMALS, 

 WHICH SEEM TO CONSTITUTE A NEW CLASS OF ORGANS.* 



By Professor Rudolph Wagner of Getting en. 



IT is well known that it has not yet been ascertained whether the sting- 

 ing or burning power of Medusa, is to be ascribed to a corrosive liquid, 

 or to a mechanical injury. I think my investigations enable us to ap- 

 proach more nearly the decision of this question. 



The origin of the stinging is, at all events, to be sought for in the 



* From the Archiv fur Naturgeschichte, 1841, Translated in Professor Jameson's 

 Edinburgh New Philosophical Journal for January 1842. 



