ON MICROSCOPIC DISCOVERY. 



(J07 



hence called diffused circulation. The most 

 favourable subjects lor viewing this are the 

 larva of the ephemera, larva of hydrophilus, 

 small dysticus, &c. In several of the polypi- 

 ferous zoophytes, as the tubularia indivisa, 

 sertulariae, campanulariae, plumularias, &c. 

 Mr Lister has, by means of the achromatic 

 engiscope, discovered a circulation to exist, 

 which in many respects resembles that in 

 plants.'' We notice in the serum of the blood, 

 when microscopically examined, two distinct 

 kinds of bodies, named glubules and discs ; and 

 accordingly as the one or the other preponde- 

 rate in the fluid mass, the vital stream is 

 healthy or diseased. The globules appear to 

 be the true particles of the blood, and the discs 

 a simple cohesion of a number of these into a 

 circular plane ; a certain proportion of these 

 discs may probably give impulse to and assist 

 the circulation, whilst an undue quantity may 

 render the motion either too tardy or too vio- 

 lent. " Upon submitting the blood to the mic- 

 roscope, a remarkable fact will strike every 

 observer, viz. there will be seen a continual 

 motion of the globules, as if they were acted 

 upon by some unknown agency. This motion 

 appears completely vibratory, like a balance 

 which has received an impulse. It is difficult 

 to account for this phenomenon, but the fol- 

 lowing hypothesis is hazarded ; this seeming 

 tendency to motion in the globules may be 

 a material assistance to the impulse given by 

 the heart, whose mere mechanical force, (how- 

 ever great,) appears hardly sufficient to propel 

 the globules through such inconceivably mi- 

 nute ramifications, through which we know 

 it does pass, previous to reaching the organ of 

 circulation by the large veins." 



We now direct oar remarks to the structure 

 of insects and their transformations, from which 

 we shall pass to a slight review of purely mi- 

 croscopical insects, or such as require the mag- 

 nifier to develope their entire figure: these 

 points accomplished, the present chapter must 

 be taken as complete. 



The eggs of insects " assume a vast variety 

 of forms: some are furnished with covers, the 

 surfaces of many are elegantly embossed or 

 fluted, whilst others, as those of the bug, (ci- 

 mex lectularius,) have their surface curiously 

 granulated." ''The eggs are contained and 

 arranged in the body of the insect, in vessels 

 which vary in number and figure in different 

 species. It is a general rule, that eggs do 

 not increase in size after they are laid ; among 

 insects, however, we find an exception to this; 

 the eggs of the tenthredo of Linnaeus increase 

 after they are laid, but their shell is soft and 

 membranaceous. The eggs of insects differ in 

 their colours ; some may be found of almost 

 every shade, of yellow, green, brown, and 

 even black." The eggs of the lion puceron 



are deposited on the leaves o'f the plum-tree, 

 and several other trees, in clusters of ten or 

 twelve. Each egg has a filament attached to 

 it; and sometimes the egg bursts, in which 

 state it resembles a minute flower with its 

 stem. These flower-like forms are the shells of 

 those eggs from which the insect has emerged. 

 " Divine Providence instructs the insects, by 

 a lower kind of perception, to deposit their 

 eggs not only in saiety from their numerous 

 enemies, but also in situations where a suffi- 

 cient quantity of food is on the spot, to sup- 

 port and nourish the larva, immediately on 

 breaking the shell. Some deposit their eggs 

 in the oak-leaf, producing there the red gall ; 

 others choose the leaf of the poplar, which 

 swells into a red node or bladder. The leaves 

 of the veronica and cerastium, are drawn into 

 a globular head by the eggs of an insect lodged 

 therein. In the Lapland Alps there is a fly 

 covered with a downy hair, called the rhein- 

 deer gad-fly ; it hovers all day over these ani- 

 mals, whose legs tremble under them. They 

 prick up their ears, and flee to the mountains 

 covered with ice and snow, to escape from a 

 little hovering fly, but generally in vain, for 

 the insect but too soon finds an opportunity to 

 lodge its egg in the back of the deer ; the 

 worm hatched from this egg perforates the 

 skin, and remains under it during the whole 

 winter : in the following year it becomes a 

 fly. The gnat, the ephemera, the libellula, 

 and the phryganea, hover over the water all 

 day to drop their eggs, which are hatched in 

 the water, and continue there all the time they 

 are in the larva state. The gnat lays but one 

 egg at a time, which she deposits on the water 

 in a very ingenious and simple manner ; she 

 stretches her legs out, and crosses them, thus 

 forming an angle to receive and hold the first 

 egg, a second egg is soon placed next the first ; 

 then a third, and so on, till the base is capa- 

 ble of supporting itself ; these, as they come 

 to maturity, sink deeper. The fecundity of 

 insects exceeds in an astonishing degree that of 

 all the productions of nature. The follow- 

 ing is an experiment of M. Lyonet on the 

 generation of a moth which comes from 

 the chenille a brass e : out of a brood of 350 

 eggs, produced by a single moth of this kind, 

 he took eighty, from which he obtained, when 

 they were arrived at their perfect state, fifteen 

 females ; whence he deduces the following 

 consequence : if eighty eggs give fifteen females, 

 the whole brood of 350 would have produced 

 sixty-five ; these sixty-five, supposing them 

 as lertile as their mother, would have pro- 

 duced 22,750 caterpillars, among which there 

 would have been at least 4265 females, who 

 would have produced for the third generation 

 a million and a half of caterpillars. It is not 

 surprising, therefore, that these insects should 



