METAZOA INSECTA. 413 



The Euplexoptera are placed by many entomologists 

 among the Orthoptera, the next order to be described, 

 but it will be seen that, while they possess certain charac- 

 ters in common with that order, they are in other essen- 

 tial respects very dissimilar. 



Until at least there is more knowledge in regard to the 

 life history of the Euplexoptera it seems better to place 

 them in a distinct order next the Orthoptera. 



Order 7. ORTHOPTERA. 



The ancestors of the Orthoptera or straight-winged 

 insects are found in the Carboniferous and possibly in 

 the Silurian formations. PI. 1003 represents one of 

 these primitive forms, Progonoblattma columbiana Scud- 

 der, which is related to the Blattidae or cockroaches of 

 to day. 



The body in these ancient cockroaches was elongated 

 and the thoracic segments were of nearly equal size, 

 while the junction of the thorax and abdomen was broad. 



The antennae were thread-like and the mouth parts 

 were of the biting type. The legs were adapted for run- 

 ning, and the two pairs of wings were of more nearly 

 equal size and texture than the wings of their descend- 

 ants. The venation of these organs was less differen- 

 tiated than in modern types, though there was a general 

 resemblance, the principal veins and their branches 

 running to the outer margin. 



Some points in the embryology of the cockroaches of 

 to-day are instructive. In these cockroaches the eggs 

 and embryos are protected by an egg-case in which are 

 placed sixteen eggs or eight on each side. PI. 1004, fig. 

 i, gives an external view of this case, and fig. 2 an in- 

 ternal view showing the eight eggs on one side. Ac- 

 cording to Cholodkovsky 1 the segmentation of the 



.1 Zeitschr. f. wiss. Zool., XLVIII, 1889. 



