12 



Cincinnati Society of Natural History. 



cles, which extend or withdraw the spinneret and sheath, and give 

 them motion in various directions, and when the organ is not in use it 

 is reflexed beneath the head carrying with it the labium and its palpi, 

 and the spinneret and sheath. I have been influenced to take this 

 view of the parts by the position of the labial palpi at the apex of the 

 mentum on each side of the base of the labium. 



In one of the papers before refered to, I have stated that the spin- 

 neret is absent in the u first form," and in another that it is present in 

 a rudimentary and functionless condition. The contradiction is on\y 

 apparent, and which statement is literally true depends on what vie con- 

 sider the spinneret. The external organ (fig. 15) is totally wanting, 

 but there is a median wrinkle in the labium, which, with sufficient am- 

 plification, presents the appearance shown in fig. 16, and is the func- 

 tionless representative of the rudimentary spinneret. 



Passing now to the Maxilla, we find but little more diversity than 

 in the preceding organs, with the exception of the maxillae of the 

 genera Cemiostoma and Tischeria, to which I shall return again. Figs. 

 20-26 show the general structure, and have been selected from a multi- 

 tude of dissections to show the extent of the diversity which is found 

 in the structure of this organ. The maxillae consist of three joints 

 the basal and second of which are each armed with a single bristle, 

 always arising at the same point. The third joint is tipped with from 

 three to five minute processes; the outer lobe or palpus arises from the 

 top of the second joint, beside the third one. Itc onsists of two joints, 

 the terminal one being tipped with minute hairs and processes, varying 

 in number from four to seven, and sometimes differing in shape. 

 Like the antennae these organs (except in the genera Cemiostoma and 

 Tischeria) afford nothing of practical value in classification, though 

 there is some diversity in the number and size of the terminal hairs 

 and processes, and in the relative sizes of the joints. 



The Mandibles have already been considered; they differ in the 

 number of the teeth, and in hardness, and considerably in shape, not- 

 withstanding which I find nothing of classsificatory value. They work 

 by a ball and socket joint, and have two bristles arising on their upper 

 margin near the base, and which are never wanting in the second form^ 

 though never present in the first form of trophi. 



The Labrum is the organ in which we "find the greatest diversity 

 (figs. 56-66). There is considerable diversity of form, but I have found 

 it of subordinate value only for classification. In the "first form" of trophi 

 it is always ciliated on the inferior surface, and armed with teeth or 



