Natural-Historical Collections. 293 



Uses of the Vesicular Appendages of the Janthina. — The Janthina is a pela- 

 gic molluscuin, and moves by means of two little lateral expansions, but 

 which, though they serve for locomotion, are not sufficient to keep the animal 

 suspended in the water. Nature has, however, supplied this want by a contri« 

 vance of which we have no other example amongst the mollusca, though it often 

 occurs in the acalepha, animals of an inferior order. This contrivance consists 

 o( a dense group of little air-vesicles of a sub-cartilaginous and diaphanous sub- 

 stance, attached to tlie posterior part of the foot, and by means of which the ani- 

 mal constantly floats upon the surface of the water. 



This cluster of vesicles has, moreover, another use, now first made known ; it 

 serves also to contain the ova of the molluscum, of which we have counted as many 

 as one hundred and eighty, suspended in a line, on the inferior surface of one of 

 the vesicles. Sir Evtfrard Home, then, is mistaken when he says that the ova of 

 the Janthina are fixed around the shell by a glairy substance. 



Many learned naturalists have supposed this mass of hydrostatic vesicles to be 

 the rudiment of an operculum. Certainly this organ is absent in the Janthina, and 

 it may be allowed that the vesicular appendages supply its place by filling up the 

 opening of the shell when the animal is retracted ; but these vesicles do not ad- 

 here in the same manner, nor have the general situation of the operculum, since 

 instead of being above the posterior part of the foot, they are below it. — Rang, 

 Manuel des Mollusques, p. 25. 



Maturation of Fruit. — At a late Meeting of the Academy of Sciences, M. 

 Couverchel read a paper on this subject. After giving an analysis of the inves- 

 tigations that had already been made, he remarked in what particulars they agree 

 with his own, and then exposed the theory to which his numerous experiments 

 have led him. According to the author, two periods are to be distinguished in 

 the history of the fruit. The first comprehends its development and the forma- 

 tion of the principles which enter into its composition. In this first period the 

 influence of the plant upon the fruit is indispensable. The second comprehends 

 the ripening properly so called, and is effected by the reaction of the constituent 

 principles of the fruit. In this second period, the acids, favoured by heat, trans- 

 form the gelatine into saccharine matter. The phenomena are in this case purely 

 chemical ; they are independent of vegetable life, and, in fact, most kinds of fruit 

 will ripen after being detached from the tree. The author finds this theory so 

 much the more probable that it agrees with another series of experiments in which 

 he has been engaged, respecting the transformation of fecula into sugar. He re- 

 marked the resemblance which these two operations present ; and, submitting to 

 the examination of the Academy two new products which he has obtained in 

 treating fecula with vegetable acids, and only varying the proportion, he gave to 

 the first, which is allied to vegetable jelly, the name of normal gum, on account 

 of its simplicity, and the property which it has of furnishing only oxalic acid 

 when treated by nitric acid. The other, which possesses all the properties of 

 grape sugar, may easily be confounded with that substance. The author, to 

 prove the resemblance which he pointed out as existing between the two opera- 

 tions, maturation and the conversion of fecula into sugar, remarked that the ge- 

 latine, in both cases, always precedes the saccharine matter, and that it is the 

 first of these substances that produces ripening. M. Couverchel's experiments 

 on the juices of fruits, and in particular on the juice of the grape, appear very re- 

 markable ; and show the possibility of improving wines of inferior quality other- 

 wise than by the addition of substances foreign to their composition, and delete- 

 rious in respect to the health. He then described some of the methods which he 

 had sought for the preservation of fruit, and pointed out the circumstances to be 

 avoided in order to attain this important object. 



Essential Characters of the Roots and Stems of Plants In whatever me- 

 dium they are developed, roots are always deprived of vital knots symmetrically 



