6 BRITISH LEPIDOPTERA. 



neuration of Palaeomicra, a New Zealand genus of the Eriocephalides, 

 and that of Bhyacophila, a genus of Trichoptera. The only important 

 difference is, that in Rhyacophila there is an additional nervure arising 

 out of 4 (lower median, Meyr.) in the fore-wings, although it is interest- 

 ing to observe that this very nervure has disappeared in the hind-wings. 

 Nothing at all approaching this form of neuration is known in any 

 other order of insects, and Meyrick considers that it is highly impro- 

 bable that so complex a type could have originated twice independently. 

 It may be observed from the above summary of the latest facts at 

 our disposal on this subject, that the opinion is pretty generally held that 

 the Lepidoptera and Trichoptera originated from a common neurop- 

 terous stock. It is not probable that either originated directly from 

 the other, but it is very possible that they branched quite indepen- 

 dently, and so represent Wo distinct lines of descent, originating from 

 a common ancestral base. There is also considerable probability that 

 the Diptera originated from the same source, as this order shows 

 considerable affinity with the Lepidoptera. 



CHAPTEE II. 



THE OVUM OR EGG. 



It would appear that there is a tendency for the eggs of all organised 

 beings to assume a more or less ovoid or spherical form. Among the 

 eggs of Lepidoptera this general tendency is well maintained, and we 

 find them roughly divisible into two forms : (1) Ovoid, longer than 

 high, with the long axis horizontal, a shorter axis vertical. (2) Up- 

 right, more or less spherical, with the horizontal axes practically 

 equal, the vertical axis equal, longer, or shorter than the horizontal. 



The primeval lepidopterous egg was probably ovoid, colourless and 

 transparent, with no sculpturing on its cell wall. This form of egg is 

 practically that which is laid by the Micropterygids, Adelids, and other 

 Lepidoptera that cut out a pocket in a leaf and deposit their eggs in 

 the soft cellular tissue of the leaf. This form of egg would, if laid in 

 an exposed situation, soon undergo modifications in many directions, 

 arising from the need of protection and concealment, and it is possible 

 that, under these conditions, one may find isolated examples of almost 

 any form in any of the families, although the simplest form of egg 

 must generally be found in the lower families, and no highly-developed 

 structure can occur, except among the species of those families that 

 have undergone a large amount of specialisation and elaboration. 



The egg of a lepidopterous insect consists of an outside shell, en- 

 closing protoplasm, which is, at first, homogeneous. The shell, 

 which forms a thin pellicle, is usually divisible into a base, walls, 

 and apex. At that pole of the egg, usually termed the apex, there 

 is, as a rule, a microscopic depression, from the base of which 

 minute canals lead into the egg, and carry the spermatozoa for the 

 purpose of fertilisation. This is called the micropyle. It will be 

 at once observed that this definition, so far as relates to the micro- 



