EGGS OF BUTTEKFLIES. 7 



undergo development, which can, in some species, be readily observed 

 through a microscope. The first cells formed unite together, and 

 present some parts darker than others, and after a time the fluid mass 

 breaks away from the eggshell, and a tubular structure, which soon 

 becomes deeply segmented, forms within. The rings become distinct, 

 and those which form the head (apparently four in number) are at this 

 time much larger than the others. As development proceeds these 

 get welded together, and the hard mouthparts become visible. At the 

 same time the three segments forming the thorax have little cells 

 developed on their outside. These are the rudiments of the legs. 

 Then a great change takes place in the position of the embryo whose 

 development has thus far been traced. 



Up to this point, the embryo has been lying in a somewhat circular 

 form with the legs outside, i.e., towards the eggshell, but now it 

 gradually changes its position until the body is somewhat S-shaped, 

 the movement continuing until a complete reversal has taken place 

 and the embryo has returned once more to a circular position, but with 

 the legs now pointing towards the centre of the egg. At this time, 

 distinct patches appear on the cheeks, and gradually six black spots 

 develop on each dark patch. These are the ocelli, five of which are 

 arranged in lunular form, the sixth being isolated and at some little 

 distance from the concave side of the others. The ocelli are simple 

 lenses, and very different from the complicated structure of the com- 

 pound eye of the imago. 



During the time that this has been going on, structural changes 

 have been taking place inside the embryo. A hollow sac forms along 

 the back, and after a time this keeps up a regular pulsation. This is 

 the dorsal vessel, and the centre of the circulatory (blood) system. 

 The alimentary canal also becomes traceable, and possibly, whilst you 

 are watching, you may observe tiny silvery threads suddenly come into 

 view, which look as if they traverse the larva in all directions ; this 

 appearance is due to the sudden expansion of the air-vessels which, as 

 we can now see, start from the little spiracles along the sides of the 

 body, this respiratory (air) system having been invisible hitherto 

 because of their transparency. After this, little lines gradually appear, 

 crossing the embryo in different directions, and usually traceable to 

 little chitinous buttons from which they arise ; these are the hairs or 

 primary setae. Certain marks on the embryo also become distinct, and 

 other peculiarities may possibly be noticed. At last the embryo is not 

 noticed to undergo any further change ; its jaws are seen to move steadily 

 to and fro against a particular part of the eggshell, usually at or very 

 near the micropyle, until a little hole is made in it, the edge of which 

 the contained larva continues to nibble until it can squeeze its body 

 through the aperture. 



It is well to remember that in some of the hybernating eggs the 

 larva is formed in the early autumn, and remains all the winter in the 

 egg, hatching only with the spring, e.g., the egg of Argynnis adippe, 

 laid in July, has its embryo fully developed in less than a month, but 

 does not hatch until the following March, the egg of Adopaea lineola, 

 and possibly others, is in similar case. 



