No. I.] CONTRIBUTION TO INSECT EMBRYOLOGY. 6 J 



velopes and the wings, originated in the ancestral Pterygota. 

 But Lemoine ('87) claims that the segmentation of the Poduran 

 Anurophorus laricis approaches the superficial type, so that 

 this latter may have had a still more remote origin. It is, 

 however, hopeless to speculate on this subject till the eggs of 

 many more Thysanura and Myriopoda, including the Symphyla, 

 have been studied. 



The relations of yolk-quantity to the movements of the 

 embryo will be considered in the following paragraphs. 



3 . Blast ok incsis. 



According to Hallez ('85 and '86) " La cellule-oeuf possede 

 la meme orientation que I'organisme maternel qui I'a produite: 

 elle a un p61e cephalique et un pole caudal, un cote droit et 

 un cote gauche, une face dorsale et une face ventrale; et ces 

 differentes face de la cellule-oeuf coincident aux faces cor- 

 respondantes de I'embryon." This law was founded on a study 

 of the eggs of Periplaneta, HydropJiihis and Lociista, but it 

 finds full support in the descriptions and figures of all investi- 

 gators of insect development. ^ My own observations, based on 

 some thirty different insects, accord perfectly with those of 

 Hallez. 



In most eggs the cephalic and caudal poles are readily dis- 

 tinguishable, the micropyle being usually located at or near 

 the former. In exceptional cases, however, it is located at the 

 caudal pole. There is frequently a slight flexure in the longi- 

 tudinal axis of the egg, foreshadowing the dorsal and ventral, 

 and consequently also the lateral regions of the mature em- 

 bryo. The more nearly the Qgg approaches the spherical form, 

 as in certain Lepidoptera and Coleoptera and in the Tricho- 

 ptera, the more obscure become the relations of the egg-sur- 

 faces to the body-surfaces of the mature embryo. There is, 

 however, every reason to suppose that these relations still exist. 



The practical value of Hallez' law was shown in studying 

 the XipJddiiim &gg ; all the movements of the germ-band could 



1 The only exception is Ayers, who was undoubtedly mistaken in regard to the 

 orientation of the young CEcaiithus embryo. 



