¥HE NEPTfCULIDES. 171 



larvae rejecting the actinic or chemical rays, whilst they are the ones 

 retained by the yellow larvae, so that the light is largely robbed of its 

 power to produce pigmentation in the former class, but remains 

 unaffected, as regards this property, in the latter class. 



The intestinal canal is usually of some shade of red, yellow or green. 

 Frequently the front is of a different colour from that of the hinder part. 

 In some of the birch-feeders it is of a vivid green. The colour, of 

 course, does not rest in the intestinal canal itself, but in the contained 

 food altered by the secretions used in digestion. In cases where the 

 larvae {e.g., N. pyri and N. oxyacanthella) eat the same food, the 

 difference in the colour of the intestinal contents (red and yellow 

 respectively) must be due to the difference of the secretions. 



The pair of brown or black lines found on the dorsum of the hinder 

 segments are supposed to be renal organs. They are situated, one on 

 each side of the intestinal canal, and are best seen from the ventral 

 surface. Each is seen, under a microscope, to be resolved into a long, 

 wavy, or tortuous tube, bent upon itself in such a way that the two 

 ends lie close together at the anal extremity. They are best seen in 

 such larvae as those of N. distinguenda, etc., which show an excess of 

 pigmentation. Many of the Nepticulids are said to be double-brooded, 

 but we have a strong suspicion that some of these species produce a 

 succession of broods under favourable conditions. 



Our knowledge of the hybernation of many species is still in a very 

 unsatisfactory state. Some species, certainly, like the Eucleids, pass 

 the winter as larvae in the cocoon, pupating in the spring. Many other 

 species, e.g., N. minusculella, N. atricollis, N. decentella, N. sericopeza, 

 also hybernate in the larval stage, but appear to leave their 

 hybernacula to spin their cocoons in the spring. Many failures to 

 breed species having this habit, may be due to the fact that the vessels 

 in which their mines are kept are not tightly closed in the spring, and 

 that the larvae wander away to pupate, rather than to the usual 

 explanation that the larvae or pupee have dried up. The larvae of 

 both N. decentella and N. sericopeza appear to spin temporary autumnal 

 cocoons for hybernation, which they leave in spring in order to .find a 

 fresh situation for pupation — the former in the crevices of the bark, 

 the latter on the newly-growing leaves and keys. 



Although many species are more or less double-brooded, and others, 

 for a few months, even continuously-brooded, yet others are, in this 

 country, unfailingly single-brooded, e.g., N. iveaveri, N. agrimoniae, 

 N. rubivora and N. angidifasciella. 



Nor is the continuous-brooded habit of some species at all 

 remarkable if the shortness of their larval life be taken into 

 account. Of this Heinemann writes (Wien. Ent. Monats., 1862, 

 p. 237) : " The duration of the larval stage of some species is extremely 

 short, especially in the summer brood, yet possibly the different species 

 vary much in this respect. In the summer brood of N. malella, 

 Buchheister noticed that on a young apple tree frequented by these 

 larvae, after he had very carefully removed from individual twigs every 

 mined leaf, in thirty-six hours he already found empty mines, and I 

 have noticed similar occurrences with N. plagicolella. On the other 

 hand, of the autumnal brood of N. plagicolella, I have had larvae still in 

 the mine for five or six days after the last moult, and the same has 

 happened with larvae of N. sjjlendidissimella, N. rubivora, N, anguli' 



