102 



11 ribs unitiug into abuut Tat top. Both are of a pale pearly green when first 

 laid, indeed almost white, in Rapae the green , becomes more pronounced and 

 passes into a yellow. But in'Cardamines the green is very evanescent, passes 

 through yellow into deep orange and almost brown. It hatches on the 8th day, 

 though there is little doubt that this period will vary with the temperature. The 

 larva takes from 18 to 24 days to feed up to its full growth, the shorter period 

 being that of a larva hatched June 30, and fed during July. A still longer period 

 is probably the rule with larva hatched early in May, as must happen in most 

 seasons. It moults four times at intervals of about three days, and spends six or 

 seven days in the last skin before suspending itself for its change to the pupa. 



The newly hatched larva proceeds to a pod of from a quarter to half an 



inch long, and eats of its substance just below the stigma ; when older it is less 



particular as to the size of the pod attacked, and will eat of a nearly mature pod ; 



it feeds exclusively on the pods and their contained seeds. I never saw one eat a leaf. 



The following are the dates of moulting in two instances : — 



Hatched June 26 June 30 



1st Moult June 30 July 3 



2nd Moult '„ July 2 July 5 



3rd Moult July 5 July 8 



4th Moult July 7 July 11 



Change to pupa July 12 July 19 



In its first skin the larva is pale buff, with black head tubercles and hairs. 

 The tubercles have the arrangement that is so common throughout the whole of the 

 Lepidoptera, and which persists throughout the larva stage in most concealed 

 feeders, such as the Hepiali, some noctuee, [tineee, and tortrices. Xylophasia 

 monoglyha (polyodon) is a fine example of these typical tubercles. They are 

 four dorsal (trapezoidal), one subdorsal, and a po.st-spiracular, on either side, 

 a subspiracular, and other ventral tubercles ; the legs and prolegs are black ; 

 the length when about to moult is 3 mm, at hatching about 1| mm. In the 

 second skin it reaches 7 mm in length ; the head is a dark olive, the body 

 greenish olive, and as if overlaid by a thin white enamel. The tubercles are 

 as in first skin, but there are faint indications of some others. JEach segment 

 is divided into four subsegments, of which the first carries the anterior trapezoidal 

 tubercles, the second the subdorsal, and the third the posterior trapezoidal. 

 In the third skin the length reaches 12 mm, the colour is green shading to a 

 white lateral line of porcellanous appearance. The colouration is now indeed 

 that of the full-grown larva. The head and all the segments are clothed with 

 black dots carrying hairs. The segments are now subdivided into seven sub- 

 segments, along which these dots are arranged in regular rows ; the tubercles 

 proper are still conspicuously large amongst these — the anterior trapezoidal 

 on the second subsegment, the subdorsal on the third, and the posterior 

 trapezoidal on the fifth. In the following, namely, the fourth and fifth skin, the 

 only subsequent change is the subsidence of the original tubercles, so that only by 

 careful observation can they be distinguished from the other dots which lie in 

 regular rows along the sub.segments. 



