MECHANISM OF SUCTION IN SCHIZONEUBA LANIGERA. 311 



Heymous (1896-8) showed from embryology that the internal or posterior 

 stylets represent only part of the first maxillse. During development the 

 basal portion o£ each maxilla forms a chitinous plate, which fuses with the 

 wall of the head. The work of Muir and Kershaw (1911) has confirmed 

 this both in Homoptera and Heteroptera ; hence this pair of stylets I have 

 called the maxillary stylets, and their sclerites the maxillary sclerites. 



Bngnion and Popoff (1911) consider the anterior or dorsal pair of stylets 

 also represent only part of the mandibles in Heteroptera, the basal portion 

 of the mandible forminp; a sclerite which fuses with the wall of the head. 



Meek also considers that mandibular sclerites (lorse) are present in Cicada. 



The later work of Muir and Kershaw (1911-12) on the embryology of 

 Pristliesanciis papiiensis and Siplianta shows that the mandibular sclerites 

 (so-called) have no relation to these stylets, and are not derived from them, 

 and thus I call these stylets the mandibles. The structures 1 refer to as the 

 clypeal sclerites agree in position with the lorse or mandibular sclerites 

 of Meek. 



IV. Anatomy of the Head and Mouth-parts. 

 A. External Structure. 



The head in repose is strongly deflexed beneath the anterior end of the 

 body. On examination of its anterior face, it is seen to be divided into two 

 distinct portions by a transverse suture, situated near the vertex. The 

 proximal portion, which bears the eyes and antennae, comprises the epicranial 

 region. The distal portion is conical in shape and tapers distally, forming 

 a stout, chitinous capsule which supports the trophic For purposes of 

 description I shall refer to the structure as the fore-head *. It freely 

 articulates with the epicranial region by means of thin, flexible chitin 

 (PL 24. fig. 1, a./.), which allows freedom of movement, enabling it to be 

 raised or deflexed at will. 



The epicranial region is broad and convex and is continuous at its proximal 

 end with the prothorax. 



The fore-head is strongly convex on its anterior and antero-lateral faces, 

 and is composed of several chitinous plates or sclerites. 



The post-lateral walls, vide fig. 18 (PI. 25), are flat and composed of thinner 

 chitin. 



In the distal half of the fore-head the integument folds into the interior, 

 between the sclerites^ forming well-defined chitinous folds, as indicated in 

 text-fig. 1. 



Looked at from its anterior face, the fore-head is seen to consist of dome- 

 shaped areas, vide fig. 1. 



* In a previous paper I called this structure the frous. This term is misleading. It is 

 the Vorderkopf of many German authors and for want of a better word I use the literal 

 translation fore-head. 



