1882.] " 99 



from the blades o£ the ovipositor it makes a turn of 90'^ in the mine, 

 by which the first-laid end comes to look forwards (i. e., in the direc- 

 tion of the head of the fly), and the concaye side to look upwards 

 (i. e., in the direction of the back of the fly) ; and so the position of the 

 egg comes to be exactly the reverse of what it would have been if 

 simply extruded backwards in a line with the parent. Nevertheless, 

 the convex side, or what in the case supposed would have been the 

 dorsal aspect, becomes the seat of the development of the embryo. 

 Having withdrawn the ovipositor, the fly presses together the lips of 

 the wound with the two valvular pieces between which the ovipositor 

 lies when not in use, possibly having injected some glutinous liquid 

 by means of which the aperture is obliterated. The mine is now a 

 closed cavity, and, as the egg grows, shows like a little blister on the 

 leaf. Generally no change whatever takes place in the parenchyma, 

 but in a few instances I have observed a growth of rather large 

 globular cells bursting off the epidermis covering the egg ; and 

 indicating perhaps a transition to gall-growth. I am not able as yet 

 to say positively which end of the egg is occupied by the head of the 

 embryo, but in all cases observed the ventral side of the embryo lay 

 along the convex side of the egg, development commencing as usual 

 in the Articulata (and Vertehratd) on the neural side. [v. Huxley, 

 Anat. of Invert., p. 667]. But at a certain stage in the development^ 

 the embryo will be found doubled-up in a loop with its ventral side 

 occupying the middle ; the first half of the dorsum, lying along the 

 concave side of the egg, now become straight by the growth of the 

 egg ; and the posterior half along the convex side, while head and tail 

 are in contact. 



This is the position of the Lepidopterous larva immediately before 

 hatching (P. hrassicce, Smnia cratcegatn, &c.),and how it gets into this 

 position, if it develops in the usual arthropod way, is a point which I 

 have only seen adverted to by Kowalevski. Speaking of the 

 development of Sphinx populi and Gastropacha pini, he says (Embry- 

 olog. Studien an Wiirmern und Arthropoden. Memoires de I'Acad. 

 imp. des Sciences, &c., p. 56) : — " Wenn der Eiicken schon gebildet 

 ist, biegt sich das Schwanzende des Embryo auf die Bauchseite und 

 zwar so, wie wir schon beim Hydrophilus gesehen haben. Dem 

 Hinterende folgend, dreht sich der ganze Embryo so, dass er jetzt der 

 ihn noch bedeckenden serosen Hiille den Eiicken zuwendet, und die 

 Extremitaten erscheinen nach innen gerichtet. In diesem Zustande, 

 mit fast vollstandig ausgebildeten Organen, bleibt der Embryo voll- 

 standig in dem ihn umgebeuden Dotter, den er nun vei'mittelst der 



