206 EMBRYOLOGY OF INSECTS AND MYRIAPODS 



it spins its web. Sometimes it eats remains of insects and other dead 

 animal matter. The egg batch is laid on the surface of the bark or 

 beneath a loose piece or crevice thereof. The eggs are laid with their 

 posterior poles touching the bark, the interstices between the eggs filled 

 up with excrement to the level of the lids; then a thin web is spun over the 

 batch, followed by a layer of excrement; and finally another web spun 

 over the mass. The number of eggs in a batch varies from 40 to 80, the 

 nymphs hatching in about forty daj^s. 



The germ band at first develops about the middle of the ventral side 

 of the egg (Figs. 127 A, B), but later the head moves toward the posterior 

 pole, and the band grows around the pole and up on the dorsal side. It 

 soon reaches nearly to the anterior pole, the posterior end of the band 

 recurving, while the head is in its lowest position at the posterior pole 

 (Figs. 127C,D). At the same time the appendages have already budded 

 out, the antennae and labrum appearing first, later the mandibles and 

 maxillae, and finally the legs. The labrum is at first ver}^ markedly lobed 

 (Fig. 127D). The amnion and serosa around the head region are in close 

 contact, but early in the recurved stage the posterior part of the embryo 

 sinks somewhat back into the yolk, so that, except around the head 

 region, there is yolk between the amnion and serosa. At a later recurved 

 stage the serosa secretes a complete outer membrane (Figs. 127F,G, section 

 i-j) which separates from the serosa. The amnion tears or disintegrates 

 down the median ventral line of the embryo and starts to grow afresh 

 laterally and dorsally, fusing to the dorsal remnant of the serosa. The 

 ventral part of the serosa also disintegrates. The remains of the two 

 envelopes — together with some yolk that was enclosed between them — 

 forms a substance that surrounds the appendages of the embryo up to the 

 time of hatching. The dorsal remnant of the serosa thus serves to 

 surround the yolk, while the amnion quickly grows around and encloses 

 them both (Fig. 127F). Shortly before hatching, the remains of the serosa 

 and amnion gather dorsally near the head (Figs. 127 F, G) and are absorbed 

 in the gut with the remains of the yolk just before the body wall grows 

 dorsad, to close over to complete the dorsal wall. When the embryo is in 

 its final position, it remains thus for 16 days while the musculature and 

 other internal parts develop. The nymph just before hatching is envel- 

 oped in three membranes : the vitelline membrane, the membrane secreted 

 by the serosa, and a cuticula molted by the nymph. All these are left 

 within the eggshell on hatching. The behavior and fate of the amnion 

 and serosa are thus similar to that of the Odonata or of Gryllus. 



DERMAPTERA 



The Earwig {Forficida auricularia L.) 

 The eggs of this earwig, as described by Heymons (1895), average 

 1 to 1.5 mm. in length, are rounded ovoid, and are slightly pointed at the 



