No. I.] CONTRIBUTION TO INSECT EMBRYOLOGY. 55 



III. The Indusium and its Homologues. 



In none of the Pterygota hitherto studied has there been 

 found any trace of a structure comparable to the indusium 

 of XipJiidiuni and Orchclivmni. The organ appears to have 

 been retained by the Locustidae and completely lost by the 

 embryos of other winged insects. In some of the Apterygota, 

 however, there is an embryonic organ which gives a clue to the 

 possible homologues of the indusium. I allude to the so-called 

 "micropyle" of the Poduridas. 



During the summer of '91 I was so fortunate as to secure the 

 eggs of Amirida viarith)ia in great numbers. They are much 

 larger than any of the Poduran eggs hitherto studied — so large 

 that they may be removed from their choria by means of 

 dissecting-needles and partially stained for surface views. It 

 is also an easy matter to obtain good sections. ^ When first 

 deposited the eggs are provided with a thin transparent chorion 

 and vitelline membrane, but after cleavage, which is total, is 

 completed and the blastoderm formed, a yellow, peculiarly 

 striated chitinous membrane is secreted from the surface. The 

 ^gg then enlarges till the chorion and vitelline membrane are 

 burst. The striated membrane was described by Ryder ('86), 

 but he failed to observe that it is attached to a large circular 

 ring — the " micropyle." In section (Fig. V) this organ is seen 

 to be a very decided thickening of the blastoderm which at 

 this time covers the whole yolk-mass as a single layer of 

 minute columnar cells. In the "micropyle" the cells and 

 nuclei are much enlarged and often considerably vacuolated. 

 Surface views prepared according to the partial staining method 

 show that the embryo is already faintly outlined on the yolk and 

 that the ring-shaped organ lies just in front of its head (Fig. VI). 

 The Qg^ being spherical, the embryo is curled in a semicircle 

 and the "micropyle" thus comes to lie on the dorsal surface 

 nearer the head than the tail of the germ-band. In the figure 

 a more advanced embryo is represented as spread out on a flat 



1 I mention this because the few fragmentary accounts that have been published 

 on the development of the Poduridae are based on the study of the embryo viewed 

 through the chorion and other envelopes. This has given rise to some errors 

 which I hope to point out in a future paper. 



