THE STUDY OF LIFE-HISTORY. 121 



simple, the allied interesting microscopic examination of its 

 parts. Although perhaps unfamiliar hy name, several species of 

 Chiro)wmus Avill be known to us by sight, the insects being often 

 common about our window-panes witliin doors, or seen perform- 

 ing intricate gyrations in the air without. In appearance they 

 closely resemble gnats, or mosquitoes as they are often called, 

 the similitude being so marked that there is every excuse for our 

 at first confounding the two. A rough and ready way of dis- 

 tinguishing between them is to watch the insects at rest, when it 

 will be seen that in CItironomiis the front legs are raised, and in 

 the gnats the hinder ones. A closer examination of the two 

 insects will show that the C/ttro»omHs differs very materially from 

 AnopJieli's, Cnlex, and other of the true gnats in having the 

 mouth-parts unadapted for either piercing or suction ; and, from 

 the fact also that the stomach is almost invariably empty, it is 

 conjectured that, in common with many other insects, the Chiro- 

 nonius does not feed in the imago state. It is not my intention 

 to enter into the life-history of these interesting insects, for 

 details of which it will be sutHcient to refer the student to 

 Miall's recently published works on the subject. Suffice it to 

 say that the females lay their eggs in running water, on the top 

 of which they rest, the ova requiring continuous access to the 

 atmosphere. To prevent them being carried down by the current, 

 and possibly submerged or otherwise destroyed, they are, instead 

 of being permitted to float free, deposited in long rope-like chains, 

 one end of which is firmly attached to the bank or other suitable 

 moorings, the string of eggs thus riding easily at anchor on the 

 surface of the stream. These egg-ropes, which can usually be 

 procured throughout the summer, will prove of deep interest to 

 the young entomological microscopist, for, being of great trans- 

 parency, it is possible to examine them as living objects, and 

 this, too, without preparation of any kind ; so that after exami- 

 nation they can be replaced in the water to continue their 

 development, the whole of which process occupies less than a 

 week. In from three to six days, according to temperature, are 

 hatched little red larvae, which, when full grown, attain to as 

 much as an inch in length. Their crimson colour has gained for 

 them the popular name of " bloodworms." These, too, are 

 transparent, and furnish most excellent material for the biologist, 

 since the heart, nervous system, and other internal arrangements 

 are easily examined through the clear outer body-wall. But it is 

 in the region of the nuclei of the cells which line the salivary 

 glands that our physiological problem in this species lies. These 

 nuclei will be found to be large, and, in addition to enclosing one 

 or two nucleoli, or smaller spheres, contain a peculiar elongate 

 irregularly-coiled cord, the ends of which, when two nucleoli are 

 present, are joined to both ; but should one nucleolus only be 

 enclosed, then it receives the two ends (Miall). What are the 



