HA RD WICKE'S SCIENCE- G OSSIP. 



225 



formula may be written K., S0 4 . Mg So 4 . Mg Cl 2 . 

 6 Aq., and it is found in large quantities at Stassfurt 

 in Prussia. It is a valuable manure for grass, but 

 most crops are greatly benefitted by its 

 use. 



Wood-ashes are also used as a potash- 

 manure. 



Common Salt seems to be coming 

 more and more into use. It serves as 

 a diluent of potash salts, and also 

 assists the solution of other salts in the 

 soil. 



Lime, Chalk, and Marl are all used 

 as manures, but their action has already 

 been described. 



Thus we have seen the composition 

 and use of the principal manures, but 

 there are many others used for special 

 purposes, as, for instance, manganese 

 compounds for roses, and sodium car- 

 bonate for hyacinths, which would take 

 too long even to enumerate. 



To rightly and economically use 

 manures we must know what constituents are deficient 

 in the soil, choose the best means to remedy this, and 

 apply them in such a way as to effect the most good 

 and least waste. 



CRUSTACEAN LIMB RENEWAL. 

 By Albert H. Waters, B.A., etc. 



THE renewal of lost limbs in the Crustacea is a 

 marvellous fact. One of my shore-crabs 

 [Carcinas Mcenas) got fighting with another of his 

 kindred, and came off second best in the combat, 

 losing both his claws and three of his legs. For weeks 

 he lived a miserable cripple with only five out of his 

 eight legs remaining, and in default of his lost claws 

 he was compelled to use two of his legs to feed him- 



I have had similar occurrences before, but it is 

 nevertheless very wonderful. If this be the usual 

 manner in which lost limbs and claws are renewed, 



Fig. 126. — Mutilated shore-crab mmediately after exuviation. 



Fig. 125- — Mutilated shore-crab just before exuviation. 



self with. At length he exuviated, and no sooner 

 had he done so than he appeared with his full com- 

 plement of limbs and claws. This sudden renewal is 

 where the marvellous part of the matter is. It would 

 have been less surprising, although wonderful enough, 

 had the new limbs budded and gradually grew ; but 

 to be suddenly and miraculously renewed in this way 

 seems most marvellous. 



how is it done ? One would be inclined to think 

 the greater part of the crustacean, so to speak, dies 

 before the exuviation ; for it is well-known that crabs 

 refuse food some days before they cast their shells, and 

 lose their solidity of flesh, which turns for the most 

 part soft and fluid. Nevertheless, they have strength 

 in their claws, as I know by experience, for they are 

 very tetchy at that time. It seems as if the wasted 

 part of the crab grows again rapidly, by means of the 

 blood sent from the heart, while the substance is 

 soft. 



Something of the same nature takes place in the 

 wings of moths and butterflies. We see in their case 

 a very small soft mass expand by means of the blood 

 sent through its veins, and grow larger and larger. 

 By the same influence we see the chitinous scales 

 (which the microscope shows are originally 

 exceedingly minute and rudimentary) also grow and 

 speedily harden. The muscles, of which there must 

 be a large supply in order to enable a butterfly or 

 a moth to flap it wings so energetically, seem at the 

 same time to develop, and from their soft flabby rudi- 

 mentary condition become firm and strong enough to 

 enable the insect to soar up into the air. 



Prawns exhibit the same phenomenon of renewing 

 their limbs, and the operation is performed in much 

 the same way. In no crustacean has the writer ever 

 seen the limb grow gradually, or show any signs of 

 doing so until the old shell exuviated, when the 

 process has taken place all at once. 



Cambridge. 



From Mr. P. Erine, San Francisco, we have 

 received a thoughtful pamphlet entitled, " The 

 Principles of Mechanics as Applied to the Solar 

 System " (price 50 cents). 



