8o4 THE AMERICAN NATURALIST. [Vol. XXXVIII. 



The V-shaped epicranial suture in Blatta separates the front 

 from the vertex. It thus represents the hne of separation be- 

 tween the cephalic lobes and the procephalon. 



Heymons maintains that the front alone is derived from the 

 fused cephalic lobes. The relatively excessive development of 

 these lobes would indicate that they must enter more largely 

 into the structure of the head. More weighty evidence is the 

 fact that the front is separated from the compound eyes by the 

 V-shaped suture. There is, of course, no question that the 

 eyes belong to the first segment and are developed from the 

 cephalic lobes. Moreover, in following through a series of 

 embryos we can trace the manner in which the front develops 

 by the extension of the procephalon into the angle between the 

 fusing lobes. Thus the direction of this suture— an inverted 

 V with the apex continuous with the median suture of the epi- 

 cranium — is easily explained. Heymons emphasizes his belief 

 that the suture represents the line of separation between the 

 first and second segments. But if that were the case the 

 rounded caudal margins of the cephalic lobes would on fusing 

 present a V-shaped angle whose apex would be directed cephalad 

 rather than caudad, as is really the case. 



On first sight it would seem obvious that the gena? belonged 

 to the mandibular segment. Huxley ('78) described the man- 

 dibles as articulating with this sclerite. To this, Miall and 

 Denny ('86) take exception. Comstock and Kochi also call 

 attention to the fact that the chief articulation of the mandibles 

 IS with the postgeuEe rather than with the gen^e. In the earlier 

 stages, after the mandibles have moved forward, it appears as 

 though the mandibular pleurites occupied the position of the 

 tuture genae. At the time of the rotation of the embryo, how- 

 ever, the cephalic lobes crowd forward over the dorsal end of 

 the mandibular segment, and thus the pleurites are pushed 

 back to occupy the position of the postgen^. 



t IS easy to see how, as a result of this process of displace- 

 ment ot the mandibular segment, there should remain a portion 

 -^^^^^e as the ventral articulation of the mandible. In the 

 • ^nit Hlatta the limits of this remnant are not to be distin- 

 Kuis led trom the clypeus ; but, as pointed out by Comstock and 



