1878.] 13 



One was dead, but the otlier Lad apparently only recently emerged, I 

 at once went out and cut a twig of alder, the food plant of the larva, 

 and placed it and the saw-fly under a bell-glass in the sunshine. The 

 insect, which had been hitherto very sluggish, and had remained 

 motionless in one position, at once on feeling the sunshine became 

 very lively, and flew up and down the enclosure. Soon it discovered 

 the food-plant : examined it nearly all over, and ultimately fixed upon 

 a young, half-grown leaf. At first it rested motionless in the middle 

 of the leaf, then it came close to the border, fixed the outer legs along 

 the edge, then raised the body up so that it was a little more than the 

 height of the tibiae from the surface of the leaf, which, it may be 

 added, was a little bent on one side. In this position it remained for 

 about a couple of seconds : then the abdomen was bent down, the saw 

 was inserted into the leaf, and apparently was moved up and down but 

 without being withdrawn out of the leaf ; at least, I infer this from 

 the motion of the abdomen. The saw was not put in straight, but was 

 bent a little forward ; the two leathery sheaths remained at right 

 angles to the saw itself. After being in the leaf for a few seconds, the 

 saw was withdrawn ; the insect remained motionless for a second or 

 two, and then the abdomen was bent down again, the saw inserted 

 (but I think not very deeply) into the hole already made, and the egg 

 deposited. During the egg-laying, the antennse were a little raised 

 above the height of the head, with a slight curve, and almost rigid. 

 The whole operation lasted about eighty or ninety seconds. Several 

 minutes elapsed befoi'e the next egg was laid. All were deposited on 

 the thick half-grown leaves, sometimes singly, sometimes as many as 

 three were placed on the same leaf. They were deposited close to, 

 but not touching any of, the nerves, and on the under-side of the leaf. 

 Immediately after being laid, the eggs were quite invisible ; but 

 by twenty-four hours they had swollen up very much, and wei^e easily 

 recognised as greenish oblong elevations. Eight days after being 

 deposited I extracted, with great trouble, an egg from its bed in the 

 epidermis, and on placing it under the microscope, had no difiiculty in 

 seeing the future larva curled up inside, which showed conclusively 

 that the eggs were quite fertile. I am not, however, sanguine of rearing 

 many of the larvae, because of the difficulty of keeping the plant fresh. 

 The leaf, in drying, contracts and presses in the egg, which thus is 

 killed. Experiments of this nature are best performed on growing 

 plants, and are, of course, best carried out by one living in the country. 

 In the above-mentioned paper, I expressed views unfavourable to 

 the occurrence of alternation of generations in the CynipidcB. I now 

 willingly admit that I then attached too much importance to mere 

 negative observations, and I am very glad to say that I have this 

 spring made some observations on Neuroterus lenticularis, which con- 

 firm those of Dr. Adler. 



31, Willowbank Crescent, Glasgow : May, 1878. 



