DRAWING WITH THE MICROSCOPE. 147 



diameter than the length of the insect to be drawn, 

 answers best to confine them : they may be kept quite 

 closed up, for they do not appear to me to require air to 

 support their existence. I was in the habit also of observing 

 them with a compound aplanatic microscope, having a 

 boot to slide over the objective end, so that it could be 

 introduced into the large transparent vessel filled with 

 water, which was their usual abode, and in which they 

 would remain pretty quiescent, especially when well 

 supplied with food. I must remark that Thames water 

 is utterly poisonous to nearly the whole race of aquatic 

 insects. I presume it is not necessary to say that every 

 species of camera lucida, and all the contrivances which 

 maybe used for tracing inanimate objects, are altogether 

 useless in drawing living ones. The colours of every 

 object are given as seen with the 9- 10th focus lens, having 

 its full aperture, as they appear in mere day-light, with- 

 out any artificial illumination whatever. I utterly dis- 

 approve of lamp-light for larvae ; it gives, indeed, a strong 

 outline, but confuses and more than half obliterates the 

 viscera, while it makes the colours very dingy and dull. 

 The tints of these objects become fainter and fainter, and 

 the shades darker and darker, as the magnifying power 

 is increased. I did not find it necessary to employ any 

 power beyond that of the simple 2-10th focus, in order 

 to develop the whole of their structure : superior powers 

 seem to me merely to magnify, without shewing any 

 thing about them (except the circulation) more satisfac- 

 torily, and do not take in a sufficient portion of the object 



