Trichogramma evanescens has the most imperfect structure, the least character, and the greatest affinity with the inferior species of other tribes, especially with the Mymar- ites. It has been reared by Mr. Curtis from the leaves of Aquilegia. Then comes the genus Pteroptrix, which though few in species, comprises several divisions, out of which may be formed nearly as many genera. Hence we have two divisions, one leading to Tetrastich us and Entedou, and the other tetramerous Chalcidites ; the other to the pentamerous species through Coccophagus and Aphelinus. Coccophagus scutel- laris and C. impeditus destroy the species of Coccus. Aphelinus Chaonia is parasitic on Aphis, and I have observed it infesting the aphides of the peach and of the rose. — Francis Walker ; Grove Cottage, Southgate.
Economy of the Selandria Cerasi. — At the end of September I observed several slug-worms, the grubs of Selandria (Blennocampa) Cerasi, feeding on the leaves of plum and pear-trees. It is supposed to have been introduced into America from Europe, and the following account of its habits is extracted from Dr. Harris's 'Insects of Massachussetts.' "As my own observations on this insect agree perfectly with those of Professor Peck, in the following remarks I have merely abridged and condensed his 'Natural History of the Shag-worm,' a work now out of print, and rarely to be met with. In the year 1828,1 observed these saw-flies, on cherry and plum-trees, in Milton, on the 10th of May ; but they usually appear towards the end of May or early in June. Soon afterwards some of them begin to lay their eggs, and all of them finish this business and disappear within the space of three weeks. Their eggs are placed, singly, within little semicircular incisions through the skin of the leaf, and generally on the lower side of it. The flies have not the timidity of many other insects, and are not easily disturbed while laying their eggs. On the fourteenth day after- wards the eggs begin to hatch, and the young slug- worms continue to come forth from the 5th of June to the 20th of July, according as the flies have appeared early or late in the spring. At first the slugs are white ; but a slimy matter soon oozes out of their skin and covers their backs with an olive-coloured sticky coat. They have twenty very short legs, or a pair under each segment of the body except the fourth and the last. The largest slugs are about nine-twentieths of an inch in length, when fully grown. The head, of a dark chestnut colour, is small, and is entirely concealed under the fore- part of the body. They are largest before, and taper behind, and in form somewhat resemble minute tadpoles. They have the faculty of swelling out the fore-part of the body, and generally rest with the tail a little turned up. They live mostly on the upper side of the leaves of the pear and cherry-trees, and eat away the substance thereof, leaving only the veins and the skin beneath untouched. Sometimes twenty or thirty of them may be seen on a single leaf; and in the year 1797, they were so abun- dant in some parts of Massachusetts, that small trees were covered with them, and the foliage entirely destroyed ; and even the air, by passing through the trees, became charged with a very disagreeable and sickening odour, given out by these slimy crea- tures. The trees attacked by them are forced to throw out new leaves, during the beat of the summer, at the ends of the twigs and branches that still remain alive ; and this unseasonable foliage, which should not have appeared till the next spring, exhausts the vigour of the trees, and cuts off the prospect of fruit. The slug-worms come to their growth in twenty-six days, during which period they cast their skin five times. Frequently, as soon as the skin is shed, they are seen feeding upon it ; but they never touch the last coat, which remains stretched out upon the leaf. After this is cast off, they no longer retain their slimy appearance and olive colour, but have a clean yellow
