74 PROC. ENT. SOC. WASH., VOL. 24, NO. 2, MAR., 1922 



in Fig. 29, where it may be seen that the seta-like structures may 

 become broader and exhibit a tendency to become serrate upon 

 one side. In Fig. 25, the endofimbrium, or mesal fringe, of the 

 second segment of the maxilla of the amphipod crustacean 

 Talorchestia is seen to have become differentiated into a tooth- 

 like spine labeled " a " and a series of somewhat broader flattened 

 processes or lacinulae, " le, " which exhibit a tendency to become 

 serrate, or "pectinate," on one side. In the isopod crustacean 

 Trichoniscus, shown in Fig. 22, there occurs in the median fringe 

 of the second segment of the maxilla, an elongate midappendix, 

 "b," which is apparently a modified member of the median 

 fringe. In Fig. 23 of the maxilla of the amphipod crustacean 

 Gammarus, the endofimbrium of the second segment has become 

 differentiated into a group of laciniadentes "a," or tooth-like 

 processes, a midappendix labeled "b, " and the lacinulae, "le," 

 which are "pectinate" on one side, and suggest very strongly 

 the condition occurring in the apterygotan insects next dis- 

 cussed; and having determined the nature of these structures 

 in Crustacea, we are now in position to determine the nature 

 of their homologues in insects. 



If one compares the mesal fringe, or endofimbrium, of the 

 stipes (or second segment) of the maxilla of the apterygotan 

 insect Tetrodontophora shown in Fig. 24, with the mesal fringe 

 of the second segment of the maxilla of the crustacean Gam- 

 marus, shown in Fig. 23, it is a very simple matter to identify 

 all of the parts, which correspond in an astonishingly close 

 fashion, in both forms (as has also been pointed out by Boerner, 

 1909). Thus the laciniadentes or incisor processes "a" of Fig. 

 23 clearly correspond to the laciniadentes or incisor processes 

 " a " of Fig. 24, while the midappendix " b " of Fig. 23 is evident- 

 ly the midappendix "b" of Fig. 24, and the "pectinate" 

 lacinulae " le " of Fig. 23 are clearly the pectinate lacinulae " le " 

 of Fig. 24. It is likewise a very simple matter to identify with 

 the incisor processes "a" of Fig. 24, the incisor processes "a" 

 of the insects shown in Figs. 27, 28, 30, etc., while the midappen- 

 dix "b" of Fig. 24 is apparently the homologue of the process 

 labelled "b" in Figs. 27, 28, 30, etc., and the lacinulae "le" of 

 Fig. 24 evidently correspond to the processes labeled "le" in 

 Figs. 27, 28, 30, etc.; and it is quite evident that the lacinial 

 structures (i. e. those borne on the second segment or stipes of 

 the maxilla) correspond, even in their minutest details, through- 

 out the sub-class Apterygota, and it is folly of Handlirsch, 1908, 

 to attempt to divide the apterygotan insects into several 

 "classes," since the great similarity among them in other 

 structural details as well, would preclude such a course of pro- 

 cedure on the part of any one familar with the structure of the 

 Apterygota in general. 



