Insects. 1235 



skin, entirely free from viscidity. They change also in form, and become proportion- 

 ally longer ; and their head and the marks between the rings are plainly to be seen. 

 In a few hours after this change, they leave the trees, and, having crept or fallen to the 

 ground, they burrow to the depth of from one inch to three or four inches, according 

 to the nature of the soil. By moving their body, the earth around them becomes 

 ' pressed equally on all sides, and an oblong oval cavity is thus formed, and is after- 

 wards lined with a sticky and glossy substance, to which the grains of earth closely ad- 

 here. Within these little earthy shells or cocoons the change to chrysalids takes place ; 

 and, in sixteen days after the descent of the slug-worms, they finish their transforma- 

 tions, break open their cells, and crawl to the surface of the ground, where they appear 

 in the fly-form. These flies usually come forth between the middle of July and the 

 first of August, and lay their eggs for a second brood of slug-worms. The latter come 

 to their growth, and go into the ground, in September and October, and remain there 

 till the following spring, when they are changed to flies, and leave their winter quar- 

 ters. It seems that all of them, however, do not finish their transformations at 

 this time ; some are found to remain unchanged in the ground till the following year ; 

 so that, if all the last hatch in any one year should happen to be destroyed, enough, 

 from a former brood, would still remain in the earth to continue the species. Mice 

 and other burrowing animals destroy many of them in their cocoons, and it is probable 

 that birds also prey upon them when on the trees, both in the slug and the winged 

 states. Professor Peck has described a minute ichneumon fly, stated by Mr. West- 

 wood to be a species of Encyrtus, that stings the eggs of the slug-fly, and deposits in 

 each one a single egg of her own. From this, in due time, a little maggot is hatched, 

 which lives in the shell of the slug-fly's egg, devours the contents, and afterwards is 

 changed to a chrysalis, and then to a fly like its parent. Professor Peck found that 

 great numbers of the eggs of the slug-fly, especially of the second hatch were rendered 

 abortive by this atom of existence." — Francis Walker ; Grove Cottage, Southgate. 



Note on a species of Platygaster. — It appears by the following extract from Dr. 

 Harris's ' Insects of Massachusetts,' that some species of this genus, like those of My- 

 mar and Telenomus, lay their eggs in the eggs of Lepidoptera. Mr. E. C. Herrick 

 of New Haven, Connecticut, has made the interesting discovery that the eggs of the 

 canker-worm-moth (Anisopteryx vernata) are pierced by a tiny four-winged fly, a 

 species of Platygaster, which goes from egg to egg, and drops in each of them, one of 

 her own eggs. Sometimes every canker-worm in a cluster, will be found to have been 

 thus punctured and seeded for a future harvest of the Platygaster. The young of this 

 Platygaster is an exceedingly minute maggot, hatched within the canker-worm egg, 

 the shell of which, though only one-thirtieth of an inch long, serves for its habitation, 

 and the contents for its food, till it is fully grown ; after which it becomes a chrysalis 

 within the same shell, and in due time comes out a Platygaster-fly, like its parent. 

 This last transformation, Mr. Herrick found to take place towards the end of June, 

 from eggs laid in November of the year before, and he thinks that the flies continue 

 alive through the summer, till the appearance of the canker-worm-moths in the 

 autumn affords them the opportunity of laying their eggs for another brood. — Francis 

 Walker ; Grove Cottage, Southgate, October, 1845. 



Note on Pteromalus puparum. — This insect appears to have two generations in the 

 space of a year, one requiring nine months (from September to July) to attain perfec- 

 tion, the other three months (from July to September). It is found throughout 

 Europe from North to South, and is also common in Canada and the United States. 



