Observations- on the Turnip Saw- Fly. 375 



black, as well as a varying line along the back, being the ali- 

 mentary canal^ thus they change their skins three times, at in- 

 tervals of from six to seven days. When full grown they are 

 often three-quarters of an inch, rarely an inch, long, and about 

 as thick as a crow-quill, but frequently do not attain to more than 

 half an inch in length ; and after changing their last skin they 

 decrease in size : this takes place in about three weeks from their 

 birth, but when well fed in confinement, they have arrived at ma- 

 turity in nineteen days. 



The full-grown caterpillars are nearly cylindrical, not in the least 

 hairy, and composed of twelve segments besides the head ; each seg- 

 ment is covered with minute warts, and formed of six or seven rings of 

 muscles, which give them a wrinkled appearance, and there are plaits 

 of muscles on the sides (figs. 2) ; the head is much smaller than the body, 

 especially the thoracic segments, which are a little inflated, the remainder 

 taper slightly to the apex ; the face is orbicidar and pubescent (8), with 

 a short conical six-jointed antenna seated on each side near to the base 

 of the lip (c), and above each is a minute black hemispherical eye {h) ; 

 the upper lip is horny, semicircular, and notched in front (e) ; the jaws 

 are very strong, horny, and subtrigonate, one with two, the other with 

 four unequal teeth at the apex (/) : maxillse (g) with a leathery 

 lobe, and a smaller one on the inside, pectinated at the apex (*) ; the 

 feelers are short, conical, and five-jointed {h) ; chin abbreviated, pro- 

 ducing two very short conical feelers composed of three joints, the 

 second notched, with a curved spine on the inside (I); the under lip 

 is fleshy, rather large, notched in the centre, where there is a small 

 lobe {k). The larva is furnished with twenty-two legs, the 'six pec- 

 toral are short and horny, formed of five joints, and terminated by a 

 minute claw (2a) ; the fourth segment has no legs, but the seven fol- 

 lowing are each provided with a pair of short cylindric ones, and the 

 apical segment has a fleshy pair at the extremity, with which the animal 

 can hold very fast. 



The larvae delight in the sun, and lie curled up upon the leaf 

 (2*) enjoying its piercing rays, and from this capability of endur- 

 ing heat, as well as from their colour, they may well be designated 

 " the negro caterpillar.'' When they feed they either fix them- 

 selves by their six pectoral feet to the edge of the leaf ('2 j), or 

 begin to eat off the surface for a small space, when they perforate 

 the other cuticle, making a hole, which they enlarge until it is 

 one or two tenths of an inch in diameter, and as the leaf grows 

 this increases, provided the whole leaf is not consumed, so that, 

 when the succeeding brood is hatched, abundance of secure 

 niduses are thus provided for their eggs. Mr. Newport dis- 

 covered that whilst they were in their first skins they had the 

 power of emitting a silken thread, to let themselves down when 

 shaken from a leaf, like the caterpillars of the geometrae and 

 smaller moths, which enables them to regain their position after 



