Burgess.] 292 [January 23, 



ner. The membrane, where it Is united with the fork, is delicate 

 and elastic, thus permitting the fork to be projected forwards or 

 drawn back at will. Within the head the fork is held in position by 

 muscles inserted on its base (fig. 7, m., m. 1 and ??2. 2 ), which unite it 

 with the lobe and stipes of the maxilla, and by a ligament which 

 runs backwards to the top of the head. Of these muscles, one (figs. 

 5 and 7, m.) is inserted on the base of the lobe; two others, m. x and 

 m. 2 , are inserted apparently within the stipes; by their contraction 

 the fork is thrown forwards out of the mouth, or moved about. The 

 backward running cord (%•), which is double, is apparently neither 

 muscular, nor the tendon of a muscle, but simply an elastic ligament 

 to draw the fork back, and probably the membrane pierced by the 

 fork aids in the same movement. The fork is still farther held in 

 place by the flexor muscles of the stipes and lobe which pass behind 

 it, and serve to bind it down against the lobe (fig. 6, mm.'). The 

 insertion of these muscles on the framework of the head can be seen 

 in figure 4, mm. 



The general shape of the fork, and its relations to the rest of the 

 maxilla, can be seen from the figures and their explanations, better 

 than described. It is hollow throughout, but the cavity tapers away 

 toward the base, the contraction beginning at the point of union be- 

 tween the membrane and the fork. At the same time the surround- 

 ing wall grows thicker, while the wall of the distal portion is of equal 

 thickness. On the inner portion, moreover, the wall becomes more 

 delicate, and, except the immediate lining of the cavity, colorless. 



In all the species of Psocidas I have examined, the outer tine of 

 the fork is longer than the inner. Usually the tips of the tines are 

 truncate, and the surface thus formed is often deeply concave. 



These insects are found on bark, old walls, fences, etc., and feec^ 

 on decaying vegetable matter. Atropos, as is well known, lives on 

 the paste in old books and boxes, as well as the specimens of ento- 

 mological cabinets. Why they should need an oral structure so 

 peculiar I do not know, but the mechanism of the fork indicates that 

 it is used as a sort of pick. 



In the maxilla we have recognized cardo, stipes and outer lobe, 

 and one naturally asks if the fork is the homologue of the inner lobe 

 of the typical maxilla, or an independent organ ? At present I must 

 incline to the latter view, although some may regard the absence of 

 anything else to represent the inner lobe as sufficient evidence of 

 their homology. But there is no articulation of any kind between 



