228 M. E. Haase on the 



half of all the species known from the Carboniferous forma- 

 tion are to be referred to the Blattida3. 



As the gradual embryogeny of the insect-body distinctly 

 shows, its constitution is to be carried back to the scheme 

 which was drawn up by B. Hatscliek * for the origin of the 

 Annelid from the trochophore. But as the structure of the 

 fully-developed insect-embryo is at the same time more 

 sharply defined in its elements than in the case of the Anne- 

 lida, IVIyriopoda, and Crustacea, and above all is subject to 

 no variations in the number of its segments, it is desirable to 

 modify somewhat Hatschek's more generally applied denomi- 

 nations of the constituents of the body for the Hexapoda. 

 Thus the expression !' frontal piece " may be substituted for 

 Hatschek's "head-segment," as this only forms the head of the 

 insect in conjunction with the jaw-bearing metameres. Fur- 

 ther, in consequence of the definitely fixed number of the abdo- 

 minal segments in the developed embryo of insects, Hatschek's 

 " end-segment " represents no indifferent terminal portion, 

 as it does among Annelida, Crustacea, and many Myrio- 

 poda. By the complete suppression in the mature embryo 

 of any indefinite anterior girdle acting as a gemmiparous zone 

 there' rather remains only of the terminal segment a terminal 

 section incapable of further development of segments, which, 

 as it bears the anal aperture, may be characterized as the 

 " anal piece." 



Consequently the body of the mature embryo of the 

 House-cockroach consists (1) of a frontal piece which bears 

 as a central process the labrum and as lateral appendages the 

 antennary lobes, shows no primitive- vertebriform rudiments 

 of the secondary body-cavity, and is perforated posteriorly 

 by the orifice of the mouth. The originally ventral position 

 of the antennas, which has been so often cited in evidence of 

 their limb-nature, probably only corresponds to the place of 

 their first origin, and therefore does not carry with it their 

 equivalence to the persistent ventral pedal appendages. 



Behind the frontal piece comes (2) the definite number of 

 true metameres, with bilateral, primitive-vertebral founda- 

 tions of the secondary body-cavity and ventral pedal appen- 

 dages. Of these segments the first three advance towards 

 the frontal piece and their appendages become jaws ; in this 

 way the head of the insect is produced. Behind these follow 

 three thoracic or mesosomatic segments, with the thoracic legs, 

 and finally the abdomen, composed of ten true metameres, 

 the early-indicated embryonic limbs of which soon disappear. 



* Arbeit. Zool. lust. Wien, i. (1878) p. 77. 



