Nos. 455-456-] 



HEAD OF BLATTA. 



805 



Kochi, in Gryllus and in Corydalis there persists a definite scle- 

 rite. These authors have shown that this sclerite bears the 

 same relation to the articulation of the mandible as does the 

 antecoxal piece to the coxa of a thoracic leg, and they have there- 

 fore called it the antecoxal piece of the mandible. 



Along the caudal margin of the postgenic, but cephalad of the 

 invagination for the posterior arm of the tentorium, is a narrow 

 sclerite, which was first pointed out by Comstock and Kochi. 

 Believing that the posterior tentorial invagination belonged to 

 the first maxillary segment and was homodynamous with the 

 invaginations of the thoracic lateral apodemes, these writers 

 named this sclerite the anterioj- maxillary plenrite. A similar 

 narrow sclerite lying parallel with the first, but caudad of the 

 tentorial invagination, they called the posterior maxillary plenrite. 

 We have seen that the posterior arm of the tentorium belongs 

 to the labial segment. The position of its opening in the adult 

 insect — almost directly over the cardo of the first ma.xilla — is 

 due to the cephalo-mesal growth of the paired labial rudiment, 

 as well as to the backward pushing of the maxilte at the time 

 of rotation. Thus the sclerite lying caudad of this opening 

 belongs, not to the maxillary but to the labial segment, and 

 should be known as the labial plenrite. The sclerite lying ceph- 

 alad of the opening may retain the name of maxillary pleurite. 



However, we cannot restrict the maxillary pleurite entirely to 

 this narrow sclerite. There early takes place a fusion of the 

 pleurites of the mouth part region. The position of the pos- 

 terior tentorial invaginations serves to mark the anterior limits 

 of the labial pleurite, but the extent of the mandibular and the 

 maxillary pleurites can only be judged from the relations of their 

 appendages. In an embryo of about the sixteenth day, as may 

 be seen from Figure 10, the maxillary pleurites exceed in size 

 either of the others. Though the rotation of the embry> resu ts 

 in a displacement of the maxilte, I do not believe that their 

 pleurites become reduced to the narrow, imperfectly demarcated 

 sclerites which have been designated as the maxillary pleurites. 



We have seen that a portion of the deutocerebral segment, 

 bearing the antennas, is more or less clearly marked off from the 

 remainder of the germ band, even in the earlier stages. I 



