July 18, 1884.] 



♦ KNOWLEDGE ♦ 



4» 



THE ENTOMOLOGY OF A POND. 



By E. a. Butler. 



THE MIDDLE DEPTHS {continued). 



ABOUT a month after the hatching of the eggs, it is 

 time for this aquatic life to close, and an existence 

 less cross and far more ethereal now lies before the little 

 creature, which has, however, by this time nearly completed 

 the cycle of its mortal life, and so has but scant oppor- 

 tunity left to enjoy the greater freedom and pleasures 

 which the acquisition of superior powers will bring. 

 Within that ugly, limbless pupa case has been formed a 

 delicate, long-legged, feathery-horned, two-winged, sylph- 

 like being, which, like the Prince iu the old story of 

 " Beauty and the Beast," is but waiting the removal of its 

 hideous disguise to appear in all its rightful elegance and 

 grace. The moment of deliverance having at length 

 arrived, the pupa tail is brought up level with the surface, 

 a considerable part of the thorax being thereby caused to 

 rise above the water. The skin then splits between the two 

 horns, and the imprisoned fly begins to emerge at the opening. 

 This is the most critical moment in its whole career, for 

 with head and thorax released, but legs still encumbered 

 by their encasement, the creature is perfectly helpless and, 

 at the same time, rather top-heavy, so that a sudden gust 

 of ■wind may in a moment capsize the tiny boat and dis- 

 appoint the hopes of the half-liberated fly, which can then 

 look forward to nothing but a miserable death by drown- 

 ing. If, however, no such mishap occurs, the struggling 

 insect gradually drags out first one pair of legs and then 

 another, and then, leaning forward, rests them on the 

 water and draws out the third pair : then making use of 

 the empty pupa skin as a sort of canoe, it soon dries its 

 wings and mounts aloft to join its companions, who every- 

 where around are at the same time putting on their adult 

 costume. In their society we will leave it for the present, 

 hoping to meet it again later on. 



The larva' of the midges are called bloodworms, and are 

 probably familiar to everyone who has kept a rain-water 

 butt, for such receptacles often swarm with the 

 wriggling, blood-red, worm-like things. They are 

 also abxmdant in ponds, and, indeed, in any stag- 

 nant water. The remarks made above concerning the life- 

 history of the gnat apply in great measure to the present 

 insects also. These red, worm-like things, however, must 

 not be confounded with a certain red worm that also 

 inhabits fresh water, forming vertical burrows in the mud 

 of rivers ; they are gregarious, and crowd their tiny 

 burrows close together, remaining with their bodies partly 

 protruded, and thus forming large red patches upon the 

 mud, and it is amusing to see the sudden disappearance of 

 such a patch as they all sharply retreat into their holes on 

 the approach of an intruder. These, however, are not 

 insects at all, but true worms, or, as they are called in 

 scientific language, annelids, and have reached, in this 

 vermiform condition, the highest stage in their develop- 

 ment. The fly, which is the parent of the red wrigglers 

 of the water-butt and stagnant pond, is called Chironomus 

 plumosus. The larva is rather more worm-like than that 

 of the common gnat, and the pupa carries some elegant 

 plumes of tine hairs on its ungainly thorax. 



There is a beautiful little creature, clear and transparent 

 as crystal, that is the larva of another member of this 

 group, and is noteworthy for the variety of curious 

 appendages it carries on the fore-part of its body. Imagine 

 an animal with a pair of arm-like bodies consisting of a 

 stem with long bristles at the end, and used to lash the 

 water, then a stout bundle of hairs movable en masse, 



then a pair of little saws, then a kind of policeman's 

 truncheon, with bunches of hairs at the end, also capable 

 of swaying backwards and forwards, and then a pair 

 of jaws and a set of bristles, and you wUl see at once 

 that Corethra ]jIu micornis, as it is called, must have enough 

 to do to manage properly all these contrivances. Such is 

 its transparency, that it may easily elude observation tiU 

 its wriggling, jerky motions Ijetray its presence. This same 

 transparency, however, aS'ords wonderful facilities to the 

 microscopist for the study of its internal anatomy and phy- 

 siology, for, by aid of the microscope, all that is going on in 

 its interior is made plainly visible. It is, of course, a 

 distinct advantage to be able to study the action of an 

 animal's internal organisation without interfering with the 

 free action of its parts, or placing it under abnormal con- 

 ditions, as there is thus less chance of mistaking for 

 essential peculiarities accidental ones, such as might be in- 

 duced by the altered circumstances. It is not to be 

 wondered at, therefore, that this creature has become 

 classic by having been made the subject of elaborate 

 investigation by more than one observer; and, indeed, 

 there are few more entrancing occupations to those who 

 have a desire to search out the secrets of nature than to 

 watch, hour after hour, under a good microscope, the 

 varied actions and vital processes of this and other 

 minutiae of animal life. It must not be ignored, however, 

 that the very transparency of parts tends also to introduce 

 a certain element of difiiculty into the investigation ; for 

 where several organs overlie one another it is not always 

 easy to trace their relative position, and it becomes neces- 

 sary to examine the object from diflerent points of view 

 before such a matter can be settled. 



Through the transparent skin of Corethra can be seen, 

 first the whole of the digestive apparatus, forming a long tube 

 of varying diameter, stretching almost from one end of the 

 body to the other ; then, on one side of this (the mouth 

 side) can be traced the greater part of the nerve system, 

 looking like a long stiing, with knots tied in it at tolerably 

 regular intervals. Where it approaches the mouth, how- 

 ever, the string divides, und sending one branch on each 

 side of the throat tube, terminates on the opposite side of 

 the digestive tract in a double mass of nervous matter, 

 which is all the representative of brain the poor creature 

 possesses. Then all down the liack (to be traced with a 

 little more difficulty, on account of its extreme transparency)' 

 is the " dorsal vessel," as it is called, which is an insect's 

 equivalent of a heart. Those who have kept silkworms- 

 or other pale, smooth-skinned caterpillars, will probably 

 have noticed this apparatus as a dark line running 

 along the back just underneath the skin, and alternately 

 contracting and expanding from behind forwards at the 

 rate of from forty to fifty pulsations per minute ; in the 

 jiresent insect the pulsations are not so rapid, being only 

 about twelve per minute. Then there can be seen the 

 numerous oblique bands of muscles by which it is enabled 

 to efiect its wriggling movements, as well as those strips by 

 which the motions of its various appendages are controlled. 

 Again, at each of two places, one near the head, the other 

 much farther down, will be noticed a pair of black bags, 

 which are air-receptacles connected with the system of breath- 

 ing-tubes distributed over the body ; the tracing of these 

 latter, however, is, on account of their extreme minuteness- 

 a matter of much more difiiculty. At the tail there are two 

 tufts of feathery hairs, one at the end, the other at the side •. 

 small though they are, the hairs are hollow, and connected at 

 their base with the tracheal system, and, whatever other 

 function they discharge, they evidently take part in that 

 of respiration. All these aquatic fly larv.-e are more or less 

 transparent, but we have chosen the present for more de- 



