142 The Microscope. 



tion of it was sure to be in the field of view when the 

 microscope's tube was lowered.* 



A tadpole cannot be arranged in exactly the same 

 manner as a stickleback ; for if it be tied down by 

 merely placing it on the glass, with cotton over it, the 

 circulation stops, because this creature does not 

 naturally lie on its side, its body being flat horizon- 

 tally rather than vertically (see c, d, No. 24). But if 

 cotton be placed both over and under it, it will be 

 secured, and the circulation will remain free. The 

 cotton should be left thin at e, that the tail may not 

 be too high above the level of the slide. The tadpole 

 should be laid somewhere about /, then turned over, 

 and it will generally come right with its tail laid 

 properly on the slide. The cotton can then be secured 

 as in the case of the fish. The tadpole's tail-fin is 

 somewhat liable to become too dry, to the detriment 

 of the circulation; it is therefore a good plan to lay 

 a thin scrap of glass over it to keep in a drop of 

 water which may be placed between; and this can 

 also be adopted with the fish. 



The arranging of the frog involves much more 

 trouble, but being a most interesting and indeed 

 splendid object, it is worth taking some pains to 

 exhibit it. When once it is arranged, too, there is 

 none which can be shown with more certainty ; and 

 the frog being not out of its element the while, can be 

 kept longer in view than one would like to attempt 



* The achromatic condenser is an arrangement by which the light 

 from the mirror can be directed with great clearness upon the object 

 examined, by placing an object-glass below the stage. 



