454 MANIPULATION, 



crystal will sometimes remain a considerable time before it 

 begins to change colour ; in that case, if it be touched with 

 the point of a pin, the red lines will be seen shooting very 

 beautifully from the point of contact. For a knowledge of 

 this beautiful microscopic object, Mr. Varley states that he 

 was indebted to Mr. Morson." 



More recently the changes of colour in the biniodide have 

 been investigated with great care by Mr. Warington, and an 

 account of his experiments published in the first volume of 

 the Memoirs of tjie Chemical Society, to which the author 

 would beg to refer the reader, as the method of viewing the 

 crystals, both by ordinary and polarized light, is rather diffe- 

 rent from that described by Mr. Varley. The paper is also 

 furnished with illustrative diagrams, and with an account of 

 the apparatus employed for the due display of the crystals. 



Tongues of the Whelk and Limpet. — In the several lists 

 of animal structures before described, the tongue of the 

 Buccinum or whelk, and that of the Patella or limpet, and 

 other Gasteropods, have been briefly mentioned ; and as this 

 organ in these animals is of great interest to the microscopist, 

 a few hints on the dissecting and mounting of the same may 

 not be out of place here. The tongue of the whelk is con- 

 tained within a proboscis of large size, which is capable of 

 being protruded, and of being again quickly retracted within 

 itself, in the same manner as the finger of a glove ; the tongue 

 is of a horny structure, covered with spines and hooks of silica, 

 which are arranged in parallel rows ; it is sustained by two 

 long cartilages, whose extremities form two lips that can be 

 separated or approximated ; or the cartilages can be made to 

 move upon each other by the mass of muscles in which they 

 are imbedded. When the cartilages move, the spines are 

 elevated and depressed alternately; and by a repetition of 

 similar movements the hardest shells are speedily perforated.* 

 The proboscis is easily fotmd when the animal is taken out 

 of the shell ; it should be slit up with a pair of scissors or a 

 scalpel, and as soon as the tongue is reached it may be easily 



* General Outline of the Animal Kingdom. By T. Rymer Jones, F.Z.S. 

 London, 1841. 



