Enlargement of Eggs of marine Mollusca in Hatching. 247 



oxygen, at the instant of its combination with carbon, sets free 

 positive, and the latter negative, electricity, thus developing 

 an electric current in a certain direction : but this is not all ; 

 for, whilst exposed to the influence of solar light, healthy and 

 adult plants decompose the carbonic acid that has, by any 

 means, accumulated in their tissues ; retaining the carbon, and 

 evolving the oxygen ; giving rise to an electric current in a 

 direction contrary to that set in motion during the formation 

 of carbonic acid. From a consideration of these circumstances, 

 it is fair to presume that, in healthy adult plants, electric 

 currents are constantly occurring in different parts of their 

 tissues ; their direction being altered by the absence or presence 

 of light, according as carbonic acid is formed or decomposed; 

 changes which Saussure has long ago shown to depend upon 

 the presence or absence of the solar rays. 



(To be continued.) 



Art. VI. On the Enlargement of the Eggs of some marine Mol- 

 luscans during the Period of their Hatching. By John Edward 

 Gray, Esq., F.R.S., President of the Botanical Society. 



A short time ago, in a discussion on the parasitic or non- 

 parasitic nature of the cephalopode, usually found in the argo- 

 naut shells, I stated, as a reason for believing this animal to 

 be a parasite, that the shell which it inhabits, when just 

 hatched (as is proved by the size of the nucleus on the apex 

 of young specimens), must have been larger than could be 

 expected to come from the eggs which are found on the 

 upper part of the cavity of the shell containing the Ocythoe. 



In this argument I had premised that the egg of all the 

 molluscans, like the snails and other free-air-breathing mol- 

 luscans, did not enlarge their shell after being laid. Having, 

 however, from some observations which I have been able to 

 make on the egg of Buccinum undatum, found that this is not 

 the case with all the marine gasteropodes, I hasten to correct 

 my former theory, which, curiously enough, has not been 

 objected to by any of the persons who have differed from me 

 in opinion, though some of them have endeavoured to de- 

 preciate the value of the observations, by attempting to prove 

 that the real nucleus was merely a small point on the apex of 

 what I considered as that part. 



The eggs of Buccinum undatum are (like the eggs of all 

 the zoophagous ptenobranchous gasteropodes that I know) 

 included in coriaceous cases, which, in this species and 

 the allied Fiisus despectus, are oblong, and cemented toge- 



T 4< 



