1886 Insects. 



that medium. But do we know anything of the metamorphoses of those Muscidae 

 acalypterae, with their solemn progress and silent flight, whose populous tribes frequent 

 the plants of our ponds ? No ; and of the thousands of species named in the works of 

 Dipterologists, scarcely one has been surprised in the mutations of its threefold life. 

 M. Dufour has traced the history of a fact of this nature. He says : — 



Towards the end of autumn, in 1846, I discovered a larva among the Lemna and 

 Callitriche growing in the water of a marsh near Saint-Sever. It was far from being 

 microscopical in point of size, since it was from fifteen to twenty millemetres in length. 

 After having carefully observed the circumstances in which it occurred, I conveyed it 

 to my study, where I observed the same conditions as nearly as possible ; and I had 

 the lively satisfaction of seeing the larva go on well, become changed into a chrysalis, 

 and, in spite of the rigour of the long winter, the winged insect was developed in the 

 following spring. 



This larva is of a grayish colour and finely sha greened, and, like the leech, under- 

 goes considerable variation in form and apparent structure, in consequence of the ex- 

 treme contractility of its skin. Sometimes it is contracted and shrivelled up, and then 

 presents a corrugated appearance, and a somewhat oval figure ; at other times it is 

 greatly extended, and then becomes lengthened out, attenuated in front and plane be- 

 neath, and rather convex above. It possesses but eleven segments ; three cephalic, 

 three thoracic, and five abdominal. The cephalic segments are tubular, retractile, and 

 capable of being drawn one within the other like the tubes of a telescope ; they are 

 without asperities, and much smaller than the succeeding segments, within which they 

 can entirely withdraw themselves. These modifications of form entail special physi- 

 ological attributes, to understand which it is necessary to study the habits of the living 

 larva. These three segments, endowed with an exquisite degree of sensibility and 

 contractility, combine, according to my views, all the functions of the senses of other 

 animals, such as feeling, sight, taste, smell, and instinct or intelligence, although they 

 possess none of the special organs of the senses. The three cephalic represent the 

 head and the bi-articulate proboscis of the future fly. Those of the thorax correspond 

 to the three combined compartments of the perfect insect. In short, and I say it with 

 a feeling of admiration for the organic conformity, the abdomen of the fly produced 

 from this same larva, whose evolution has produced for me so much mingled solicitude 

 and satisfaction, has no more than five segments. The larvae of nearly all the Mus- 

 cidae have two pairs of stigmata ; in this, however, there is but a single posterior pair ; 

 and these afford a proof of the care taken by nature to ensure the due performance of 

 the important function of respiration in an animal of aquatic habits unprovided with 

 branchiae. These pneumatic orifices are situated at the bottom of a stigmatic hollow, 

 placed on the last segment of thebody, which segment is eminently mobile. This 

 hollow is crowned by eight large triangular lobes, all of equal size. These, in the act 

 of respiration, remain emerged, and open like a regular corolla with eight petals ; but 

 when the larva has occasion to descend, it brings together the lobes of the hollow ; 

 and the edges of these lobes are so well adapted to each other, that they hermetically 

 close the stigmatic receptacle. The orifices are in orbicular projections, into which 

 the air is admitted by means of a median aperture ; and when the integument of the 

 larva becomes thinner as it elongates, a close inspection with a lens will show both the 

 two principal tracheae which terminate in the openings, and the anterior point where 

 they anastomose and form a common canal. 



A few days after I had replaced in the water the larva which I had been studying 



