262 KANSAS UNIVERSITY SCIENCE BULLETIN. 



they meet the gense. Their outer margins meet the maxillary 

 sclerites, and their mesal sides are bounded by the frons and 

 clypeus. The sclerite extends downward for half the length of 

 the clypeus. 



The Maxillary Sclerites. (Fig. 1, mxs.) Laterad of the 

 mandibular sclerites are the long, narrow chitinized strips 

 forming the lower lateral edges of the head. These are the 

 maxillary sclerites. Viewed caudad they are much wider and 

 lighter in color. They form the boundary for the lower part of 

 the occipital foramen. The lower part projects into a mesal 

 pointed piece, the rnaxillary process (fig. 4, procx) , which in the 

 normal position covers the hypopharynx and is closely appressed 

 to the stylets. 



Mouth-parts. Before proceeding to descriptions of the in- 

 dividual organs, it may be well to note the main features of the 

 insect mouth and the modifications they have undergone in the 

 orders of sucking insects. The mandibulate mouth consists of 

 two pairs of laterally working, shear-like jaws, covered above by 

 the labrum and closed below by the lower lip, the labium. The 

 inner surface of the labrum is sometimes developed into the 

 epipharynx. The labium also bears on its inner surface a well- 

 developed ligula or hypopharynx. 



In the suctorial mouth the four jaws have elongated and be- 

 come setiform. The labrum has been greatly reduced and the 

 labium has become a canal-shaped beak inclosing the setse. 

 These homologies were long ago determined by anatomists. 

 Westwood says of the Hemiptera : "The mouth is of the pro- 

 muscid construction, the labium or canal being occasionally 

 greatly elongated and extending beneath the body, and is either 

 three- or four-jointed. The four internal delicate setae represent 

 the mandibles and the maxillae." It is very gratifying to know 

 that recent embryological work is verifying these early ho- 

 mologies. « 



The Labium. (Figs. 1 and 2.) The most prominent of the 

 C?'cad<x mouth-parts is the labium. Early investigators termed 

 the organ haustellum, rostrum, promuscis, proboscis, Schnabel, 

 or Russel, but in late years, since more attention has been given 

 to homologies, the name labium has come into favor and it will 

 doubtless remain. The labium, then, the most noticeable part 

 of the suctorial mouth, projects from the lower angle of the 



