191« 



iluir and Kershaw — Development of Moiithparts in Homoptera 



87 



held fixed to the pharynx. The "mandibular plates" or lorse lie 

 between the pharyngeal and mandibular sulci and are formed by 

 them. They are not derived from the mandibles and have no 

 relation whatever with them. The relative positions of the tro- 

 phi have changed but slightly in spite of the great change of func- 

 tion. 



Embryology shows us only that the maxillary plate is formed 

 from the basal portion of the first maxilla and the seta from the 

 distal portion. It is possible that the former represents the cardo 

 and stipes and the latter the lacinia and galea combined, or the 

 palpiger. That the palpus does not enter into the seta is evident 



13a. Attachment of mandibles to head-capsule (Plata). 

 13b. Attachment of mandibles to head-capsule (section). 

 13c. Section through mandibular sulcus. 

 13d. Attachment of maxillary seta to head-capsule (section). 



from the Thysanoptera having both seta and palpus. The two 

 small lobes at the extremity of the maxillary plate in Thysanop- 

 tera may represent lacinia and galea, in which case the seta would 

 most likely be a development of the palpiger, a conclusion one 

 would ])e led to from its position. 



The labrum is formed by the amalgamated second maxillse and 

 is homologous to the labrum of Thysanoptera. The similarity of 

 the mouthparts of these two orders is not a superficial resemblance 



