NOTES ON THE EAELY STAGES OF OEMIOSTOMA LABUBNELLA. 183' 



and elevate the anterior and posterior portions of the body. This feat 

 also shows that its muscles are well developed. The larva now mines, 

 right and left from the end of the gallery until it has eaten out a 

 round patch of the parenchyma, of a diameter of 6mm. This patch is 

 filled with black excrement, except a pale yellow line which runs 

 about half-way round the outer edge. This is where the larva lies 

 until it has assumed its fourth instar. The change of skin success- 

 fully completed, the larva soon recommences to mine. It now begins 

 to form that part of the mine which later becomes the conspicuous 

 pale brown patch that so disfigures the leaves when a laburnum tree 

 has been badly attacked by this species. The regular mine, up to this 

 stage, consists, as we have seen, firstly of a minute dark spot, secondly 

 of a short gallery, and thirdly of a larger more or less circular blotch, 

 the three portions together, in outline only, reminding the observer of 

 a balloon with the car attached at a further distance from the envelope 

 than usual. But, of course, the mine is perfectly flat, and remains 

 flat till completed. Each portion of the mine corresponds with one 

 stadium of the larva. When the larva in the balloon-like portion of 

 the mine has changed its skin and assumed the fourth and last instar, 

 it commences mining on a larger scale, and its tracks form a series of 

 arcs. In the more regular mines, in cases where the egg was laid 

 towards the base of the leaflet, the larva makes a continuous progress 

 right up to the apex of the leaflet, usually keeping one side of the mid- 

 rib, and consuming all the parenchyma contained in the upper half of 

 the space bounded by the mid-rib and the margin of the leaflet. But 

 many mines are not so favourably situated, and the larva, in order to 

 obtain its full amount of nourishment, has to mine the leaf on both 

 sides of the mid-rib. In most cases the last part of the mine so 

 involves the earlier portions that they become lost to view, or difficult- 

 to make out. This last part of the mine often measures a length of 

 30mm. with an average breadth of, say, 7mm. When the larva, in its 

 first instar, has once reached the upper surface of the leaf, it mines 

 dorsum uppermost, and continues in this position till the mine is 

 completed. The upper cuticle of the leaf, which the larva separates 

 during the process of mining, is fairly transparent, and the larva would 

 be easily seen in the mine but for the fact that it deposits almost all 

 of its excrement on this upper cuticle. The excrement is at first 

 green, but in a few hours becomes black and effectually hides the 

 caterpillar. In the last part of the mine, the larva, when feeding, 

 usually lies in a semicircle, with its head at the circumference of the 

 mine, where it bites away at the parenchyma ; its tail is also near the 

 margin of the mine. The anus is turned upwards in order to place- 

 the pellet of excrement on the upper cuticle. Hence, as the larva, 

 mines out a line from one side of the mine to the other, like the swath 

 cut by a scythe, this line is followed, a little distance behind, by a line 

 of excrement, and thus the last part of the mine is characterised by a 

 number of black arcs running across it. 



The larva in this fourth or last stadium is of a pale waxy grey with 

 a broad dark green band on the dorsum of the abdominal segments. 

 The prothoracic shield is dark grey, divided by a pale line, the usual 

 tubercles and sets are present, and there is an abundance of short pile. 

 The larva is very active when taken out of the mine and usually spins 



