NORTH AMERICAN DIPTERA. 



321 



This means, practically, that all previous investigators had com- 

 pletely misunderstood the nature of the Dipterous mouth, and puts 

 me to a strict proof of my assei'tions. To do this it may be useful 

 to state how I, not a special student in the Diptera, reached this 

 conclusion. 



In a study of the " Horn fly," Hmnaiobla serrata, the mouth parts 

 were examined and figured, to show how the "biting" was done. 

 The nomenclature adopted, agreed with that above given by Willis- 

 ton. To illustrate some lectures and papers during the Winter of 

 1889-90, several carefully prepared slides were required, and, among 

 others, the Dipterous mouth was well represented. Finally, during 

 the Summer of 1890, a lecture on the mouth structure of insects, 

 prepared as a part of a course delivered at the Cold Spring Labo- 

 ratory of Biological research, brought to my mind very forcibly, the 

 want of agreement in the line of development, for the mandibulate 

 and haustellate series. A number of diagrams, j)repared to illustrate 

 these lectures, and now adorning the walls of my laboratory, brought 

 me to a gradual comprehension of the homology which I am now 

 trying to prove. 



To understand exactly the line of investigation, it becomes neces- 

 sary to look for a moment, at the structure of the mandibulate mouth. 

 A generalized view is given by Newport's figure of Andrena, which 

 is here reproduced in order to fix the comparative 

 location of the parts, and without any guaranty of 

 correctness in detail. We find the mandibles at 

 the extreme side of the mouth, next the clypeus, 

 and above the labrum, which forms a frontal cover 

 or shield, to the base of the mouth parts. The 

 maxillary palpi are below and within ; between the 

 mandibles and the maxillse. Central, is the labium 

 with its development of ligula, paraglos.sa and 

 palpi. The mandibles have no point of attachment 

 to either maxilla or labium. The labium is called 

 the lower, the maxilla the upper jaw, but practi- 

 cally, in many cases, the two are on the same plane, 

 and, quite frequently, the labial appendages are 

 before or concealed in part by the maxillary development. 



The maxilla, illustrated by a species of Polistes, probably metricns 

 Say, is composed of the cardo, the stipes, the subgalea, the lacinia. 



Fig. I. Head of An- 

 drena. After New- 

 port. 



TRANS. AM. ENT. SOC. XVII. 



(41) 



NOVEMBER, 1890. 



