14G [December, 



equal frequency. Often we meet with two eggs lying together, evidently 

 laid by the same fly with the same orientation, in which the heads of 

 the embryos lie in opposite directions. This is in direct contradiction 

 to the dictum of Leuckart : " Der obere Pol des Eies beherbergt in 

 alien Fallen das Kopfende des Thieres " (Ueber die Micropile, &c., 

 Mullers Archiv., 1855, p. 102) . Ea,re exceptions to the rule occur also, 

 as I have already shown, in the eggs of Gastrophysa raphani. The 

 position of the dorsum and venter of the embryo, as pointed out in 

 my former paper, is itself abnormal in these eggs ; development com- 

 mencing on what should be (according to Herold, &c.), the ''dorsal" 

 side of the egg, and the dorsum of the embryo facing, and lying along 

 the " ventral " side of the egg, if the orientation of the latter is 

 determined with reference to the parent fly. To this regular 

 abnormality in Zarcea I have, however, in last summer's observations, 

 seen 3 — or at any rate 2 — decided exceptions, in which the dorsum and 

 venter of the embryo occupied the reverse positions in the egg. The 

 bilateral symmetry of this egg is so decided that it is not easy to make 

 any mistake. In one instance I found an egg in the mine, not lying 

 on its side as usual, with its transverse, shortest, diameter, but with its 

 dorso-ventral axis, vertical to the plane of the leaf, and therefore 

 causing much more distension of the mine, but without any other | 

 irregularity. A more striking irregularity I shall perhaps best 

 describe in the words of the note made at the time : "June 3rd, I have 

 just opened a marked mine of Zarcea in which I suspect something 

 unusual in the position of the embryo. It appeared to be curved round 

 the inner convex side of the egg, with the head and tail meeting or 

 approximating on the marginal or straight side. And so it is ; but the 

 incurvation of head and tail is dorsal, the venter of the embryo lying 

 along the inner convex side of the egg. The embryo appears to be 

 dead. I have taken it quite out of the mine, and the position of the 

 mandibles and of the thoracic legs leaves no doubt concerning its very 

 unusual position." Unless this position of the embryo can be explained 

 as an exaggeration of what is sometimes met with in a minor degree, 

 viz., a sort of spiral twisting of the larva upon its axis, it would 

 indicate a mode of development the reverse of what was observed in 

 all other cases, in which the doubled-up position of the embryo in the 

 egg is brought about by the veiitral incurvature and growth forwards 

 {i.e., towards the head) of the posterior extremity. In this connection 

 I may mention that, having obtained some eggs of Bumia cratcegata 

 (114 from one moth) in June last, I took special notice of the devel- 

 opment of the embryo with reference to this point, and to the theory 



