OF MICROSCOPIC OBJECTS. 133 



mentioned, because the blood-vessels are not nearly so abundant 

 as in tlie foot of the frog, &c. The stickleback is, however, pro- 

 curable almost in any place during the summer months, and may 

 be laid in a shallow trough, loosely bound as the tadpole. The 

 tail may be covered with a piece of thin glass to prevent him 

 curling it to the object-glass. The power needed with this will 

 be about the same as with the other subjects viz., half to quarter 

 inch object-glass. 



It is not absolutely necessary to go to reptiles or fishes for this 

 curious sight, as some other animals serve Very well. In the 

 wings of the common bat may be found a good subject. These 

 must be stretched out on something resembling the frog-plate 

 before described, when those parts near to the bones will show 

 the largest vessels very clearly. The ear of a young mouse is an 

 illustration of the same phenomenon, but it is very difficult to fix it 

 in a good position, as these animals are so very timid and restless., 



Amongst insects also the same law may be observed, by placing 

 them in the " cage," or " live-box," so as to keep them still, but 

 not to injure them by too much pressure. In certain larvae this 

 is particularly well shown, as that of the day-fly and plumed gnat ; 

 but in some of these the blood is almost colourless. In the wings 

 also of many insects this circulation is well seen, as in those of the 

 common house-fly ; but as these parts become dry in a few days, 

 the subject should not be more than twenty-four hours old. 



Somewhat approximating to the forementioned phenomenon, is 

 the " rotation " of fluid in the cells, or, as it is usually termed, 

 the circulation of the sap, of plants. This is shown in certain 

 vegetable growths as a constant stream of thick fluid, wherein 

 small globules are seen ; which stream flows round the individual 

 cells, or up the leaf, turning at the extremity, and down again by 

 a different but parallel channel. There is little or no difficulty in 

 showing this in many plants ; but some are, of course, better than 

 others, and require a different treatment; we will, therefore, 

 notice a few of these. Perhaps the best of all is the Vallisneria 

 spiralis, which is an aquatic plant, frequently grown in, but not 

 really belonging to, this country. As it somewhat resembles 

 grass, the leaf is not used in its natural state, but a thin section 

 cut lengthwise with a razor or other sharp instrument this sec- 



7* 



