OF MICROSCOPIC OBJECTS. 113 



" In the limpet this reserve-ribbon is of great length, being 

 nearly twice as long as the body, and the whole of it is exposed 

 to view on simply removing the foot of the animal ; nothing, then, 

 can be easier than to extract the tongue of the common limpet. 

 But, unfortunately, what you find in one kind of mollusc is- not at 

 all what you find in another. In the Acmseas, for instance, which 

 are very closely related to the limpets, and have shells which can- 

 not be distinguished, the reserve portion of the ribbon has to be 

 dug out from the substance of the liver, in which it is imbedded, 

 that organ being, as it were, stitched completely through by a long 



loop of it It might be thought a comfortable reflection 



that, at all events, one end of the ribbon can always be found in 

 the mouth ; but in many cases this is about the worst place to 

 look for it. Perhaps it may appear strange that in some of the 

 smaller species, with a retractile trunk, a beginner may very likely 

 fail altogether in his attempt to find the mouth ; if, however, the 

 skin of the back is removed, commencing just behind the tenta- 

 cles, there will be very little difficulty in making out the trunk, 

 which either contains the whole of the ribbon, as in the whelk, 

 or the front part of it, as in Purpura and Murex, where a free 



coil is also seen to hang from its hinder extremity In 



the periwinkles the same plan of proceeding, by at once opening 

 the back of the animal, is best ; and on doing so, the long ribbon, 

 coiled up like a watch-spring, cannot fail to be found. 



" In the Trochuses, and indeed in all the Scutibranchiata, one 

 point of the scissors should be introduced into the mouth of the 

 animal, and an incision made directly backwards in the middle 

 line above to some distance behind the tentacles; the tongue is 

 then immediately brought into view, lying along the floor of the 

 mouth." 



Dr. Alcock's method of dissection will be found to differ in 

 some degree from the general rules before given ; and when the 

 tongue is dissected out he washes it for one hour (shaking it now 

 and then) in a weak solution of potash. After cleaning thorough- 

 ly in water, it must be mounted by one of the methods before 

 mentioned. 



Amongst insects, especially the grasshopper tribe, are found 

 many which possess a gizzard, armed with strong teeth, somewhat 



6* 



