THE OVUM OR EGG. 



pyle being placed at the apex of the egg, is quite conventional, for, 

 although the micropyle is actually at the apex in spherical, or, as 

 they are usually termed, " upright," eggs ; on the other hand, it is at 

 one extremity of the long (horizontal) axis in ovoid, or, as they are 

 usually termed, "flat," eggs. Since the "upright" egg has more 

 probably been evolved from the " flat " form, than vice versa, it 

 follows that, when we use. the term " base " in the two forms of egg 

 for that side by which the egg is usually attached to the surface of the 

 food-plant, or other object on which it may be deposited, by the 

 parent, the sides are not homologous in the two structures. In general, 

 we speak of the side opposite the micropyle as the base. It follows, 

 therefore, that we speak of a Noctuid egg as being laid on its base, 

 and, to get rid of the anomaly, we speak of a Geometrid or Lasio- 

 campid egg as being laid on its long side, whereas, as we have already 

 suggested, the older form of egg is probably that which is laid on its 

 long side, which should then, in reality, be called the base. 



The greater number, by far, of the families which used to be 

 included under the title of Micro-Lepidoptera have " flat " eggs ; such 

 are the Micropterygids, Tineids, Pterophorids, Gracillariids, Gele- 

 chiids, Pyralids, etc. With this group the higher Geometrids and 

 Brephids, which also have flat eggs, may be considered. Another 

 important group with flat eggs, consists of the Zygaenids, Lasiocam- 

 pids, Saturniids and Sphingids. The Lepidoptera with upright eggs 

 are the Cossids, Cymbids (Chloephorids),Notodonts, Noctuids, Liparids, 

 Arctiids, Hesperids and Papilionids. There are, undoubtedly, a few of 

 the so-called Micro-Lepidoptera with upright eggs, e.g., Chrysocorys 

 festaliella, but very little is known of the eggs of these moths. 



The base of a lepidopterous egg, then, as hitherto used by ento- 

 mological authors, is a doubtful quantity. It has been considered by 

 some as that side by which it is attached to its food-plant ; it has been 

 considered by others as that side opposite the micropyle. We use it 

 in the latter sense, as tending to preserve correctly the homologies of 

 the egg structures. 



The side by which an egg is attached to any object is usually flat 

 and devoid of characteristic markings, but the walls are generally 

 sculptured in some form or other, although they are, in a few cases, 

 quite smooth. The flat eggs are, as a rule, ornamented only with 

 rough pittings, worked up in some cases into a roughly polygonal 

 reticulation ; they rarely have longitudinal ribs, although certain 

 Geometrids — Gnophids and Acidaliids — exhibit this style of orna- 

 mentation. The eggs of Geometrids offer many remarkable modifica- 

 tions in their sculpture, from the almost smooth egg of Tephrosia, 

 to the marvellous polygonal reticulation (with a white knob at each 

 angular point) presented by Eurranthis plumistraria and HemeropJrila 

 abruptaria. The Zygrenid egg is characterised by its bright yellow 

 colour, with one pole quite transparent ; the Lasiocampid egg by its 

 tiny raised points at the angulations of the finest conceivable reticula- 

 tion, and by its opalescent markings. The Sphingid egg is almost devoid 

 of markings, the micropyle often being practically indistinguishable. 



In the upright eggs, however, the ornamentation becomes much 

 more complex. The pitting takes the form, generally, of hexagonal 

 cells, and longitudinal ribs stand out from the surface of the egg, and 

 run from the base to the apex of the egg, the ribs being generally lost 



