58 NEW ZEALAND ENTOMOLOGY. 



taken, if anywhere. Its life-history is at present unknown, 

 but no doubt resembles that of the following insect. 



Family SYRPHID^E. 



Helophilus trilineatus (Plate VII., fig. i, la larva, ib 



pupa). 



This fine species occurs abundantly in all damp situations 

 throughout the summer. . Its larva may be found in 

 stagnant pools and is often met with in the mud at the 

 bottom of ditches. Its posterior segments are enormously 

 elongated, forming a telescopic breathing apparatus, com- 

 posed of two tubes, the smaller of which is capable of 

 being more or less extended at the will of the larva, which 

 is thus enabled to adjust the length of its breathing tube, 

 according to the depth of water or mud In which it 

 happens to reside. This peculiarity has given all these 

 larvae the name of rat-tailed maggots. The other segments 

 are very stout, each being furnished with a pair of minute 

 feet, and the head is also provided with two small appen- 

 dages which are supposed to be the outlets through which 

 the exhausted air is discharged by the larva. When mature 

 this insect leaves the water, forming a small oval cell in the 

 neighbouring moist earth, in which it lies with its long tail 

 folded along the breast. The skin then gradually hardens, 

 and it is finally transformed into the pupa shown at Fig. 

 ib, the conical pair of breathing-tubes on the thorax being 

 slowly protruded from two hardly perceptible warts, whilst 

 the telescopic apparatus shrinks up, its functions being at an 

 end. A variable time, dependent upon the season, elapses 

 before the perfect insect makes its appearance, but prior to 

 this occurring, a large circular plate, forming the thorax of 

 the pupa, is thrust off, thus assisting the escape of the fly, 

 which immediately ascends a plant, or other convenient 

 object, to dry and expand its wings (Fig. i). In the perfect 



