1916] Biology of Aquatic Lepidopter a 169 



represents an instar has not been determined and the discussion 

 of later instars will be left for a future paper. The full-grown 

 larva has been studied by Forbes ('10, p. 221) and the specimens 

 studied in this connection agree with his description in most 

 regards, assuming that his table of gill numbers represents an 

 average condition and not a constant one. The most striking 

 change in the later larval instars is the remarkable increase in 

 the number of gills. The maximum number of gills per segment 

 increases from two in the second instar to as many as ten per 

 segment in the full-grown larva. The total number of gills 

 increases from twenty-two in the second instar to one hundred 

 in the last one. The number of gill filaments per segment 

 increases from four in the second instar to as many as forty-eight 

 in the mature larva. The total number of gill filaments on the 

 whole body increases from forty to over four hundred. Such 

 a provision of tracheal gills would seem to be adequate for a 

 wide range of aquatic conditions. ' 



Activities of the Larva. 



Locomotion. — The young larvae are active from the moment 

 of hatching, crawling restlessly about over the egg shells and 

 the adjacent leaf surface. Locomotion on the water-lily leaves 

 consists exclusively of crawling movements. In the younger 

 instars, particularly in the first, this method of locomotion is 

 slow, often appearing awkward and inefficient. CrawHng, in 

 the older instars, is more active and vigorous and, under normal 

 conditions, constitutes a comparatively efficient form of loco- 

 motion. The efficiency of crawling as a method of locomotion 

 depends upon the character of the supporting surface. On 

 the yellow water-lily leaf, crawling is accomplished with some 

 degree of ease, except when the leaf, bearing larvae on the upper 

 surface, is submerged, a condition which seems to require extra 

 effort. Crawling on the glass surfaces of the aquaria is very 

 slow and inefficient, consisting of little more than a mere clinging 

 to the glass, and change of position is accomplished with 

 difficulty. Other surfaces of a smooth, firm nature also afford 

 difficulties in crawling. 



At no time during the larval period did the writer observe 

 any evidence of an ability to swim. In this connection, a num- 

 ber of experiments were tried with larvae of all ages but results 

 were always negative. Random, writhing movements were 



