322 



do tlie same work while the insti'ument is being withdrawn, and resum- 

 ing its jjlace in the slit. The straight gashes made by the ovipositor 

 can be invariably seen on the under side of the leaf, close by the posi- 

 tion occupied by the egg. The length of the ovipositor, to the inter- 

 nal bend, is .042 inch ; and its width, .001 inch. 



The habits of these saw-flies are sluggish. In damp or even cloudy 

 weather, they stand motionless on the under sides of the leaves. When 

 approached by the hand, they are apt to drop as if dead, and thus 

 escape. They never, in such weather, attempt to fly away. In sunny 

 weather, they may be seen on both surfaces of the leaves ; and, on tak- 

 ing alarm, will sometimes fly away. The insect is willing to alight on 

 the leaf of any tree, but makes a strict selection In depositing its ova. 



These flies were first observed on the 5th of June. By the 8th, they 

 had apparently diminished in numbers ; on the 9th, they were moder- 

 ately numerous, and active on some of the trees; on the 10th, very 

 few were to be found; on the. 11th, none. Nevertheless, one or two 

 were observed near the close of June, and one or two in July. 



The following observations were made on the development of the 

 embryo : — 



June 7, The ovum is .03 of an inch in its longer diameter, and 

 .014 in its shorter. The form is a prolate ellipsoid, flattened on one 

 side. The contents are simply granular. 



June 8. Under a power of 230 diameters, the contents of the egg- 

 cell consist simply of small globules, the whole mass of which, under a 

 compressor, seems to be divided into large irregular areas. On certain 

 sides, also, are presented some inequalities, like convolutions, as if the 

 embryo were beginning to receive shape. 



June 9. The embryo can be discerned doubled together, and pre- 

 senting already distinct traces of articulations. 



June 10. Embryo apjaears clearly as an articulate, doubled together 

 with its back next the periphery. The jilace of the eye is a dark- 

 brown spot. The oral organs are clearly developing, and the legs are 

 beginning to protrude in distinct sacs. When slightly compressed, the 

 vitelline membrane bursts, and the traces of organization dissolved at 

 once into a multitude of granules floating in a watery fluid. 



June 11. Pedal protuberances well developed, and claws beginning 

 to appear. The head distinctly isolated from the body, and the oral 

 apparatus C|uite distinct ; at intervals, also, the embryo squirms in its 

 nidus, and occasionally a single foot protrudes and retracts itself 



June 12. Movements of the embryo frequent. Aortic contractions 

 quite regular, at the rate of 30 per minute : occasionally they intermit 

 for a minute or two. The contractions are always seen immediately 

 after the efibrts at motion. 



June 13. Embryo appears stronger, and makes more energetic mo- 



