202 INSECT TRANSFORMATION 



elongate sub-cylindrical maggot, headless like all its tribe, but 

 with seven pairs of ventral prolegs along the body ; the cuticle 

 is rather closely covered with minute spines presenting thus a 

 roughened aspect. From the hinder end projects the long 

 " rat-tail " a flexible outgrowth of the body into which the 

 tracheal trunks are prolonged, and having a more slender and 

 delicate distal region which can be telescoped into the thicker 

 proximal portion, or thrust out so as to reach the surface film 

 while the body of the maggot remains deeply submerged in 

 water. At the extreme tip of this spiracular tail is a circlet of 

 fine sharp spines by means of which the surface film is caught 

 and depressed, connexion being established between the atmos- 

 phere and the maggot's air-tube system. Thus obtaining con- 

 tact with the pure upper air, the larva of Eristalis is able to 

 live submerged in the foulest liquid where it finds abundant 

 organic food-supply. Ditches containing " retting ' flax, 

 waters heavily contaminated with sewage, even the fluids 

 resulting from the decomposition of large animal carcases have 

 been known to serve as suitable surroundings for the develop- 

 ment of rat-tailed maggots. 



When fully grown, the drone-fly maggot buries itself in the 

 mud and its cuticle becomes shrunken, hard, and dark, forming 

 the protective puparium (Fig. 105 b) within which the pupa is 

 encased after the reconstruction of its parts. The puparium 

 has the shrivelled " tail " still attached to its hinder end, but 

 this appendage no longer serves for breathing. A pair of 

 processes on the thorax very small during larval life are 

 now standing out conspicuously ; these (s) are spiracular tubes 

 communicating with the air-tube system of the enclosed pupa. 

 On the rounded lid of the drone-fly puparium, which breaks 

 away to allow the emergence of the fly, another pair of pro- 

 cesses, the " anterior horns ' (c), are visible. These have 

 their surfaces surrounded by alternating ridges and grooves, so 

 that they look like tiny screws ; they have no known 

 connexion with the insect's special mode of life. 



The above-mentioned examples must suffice for illustration 

 of the various adaptations of insect larvae for life in water. 

 From the point of view of the study of environment it is 

 interesting to notice how such insects make use of two diverse 

 spheres of habitation in the preparatory and perfect stages of 



