rOLSOM: MOUTH-PAETS OF ANURIDA MARITIMA. 95 



Packard ('71, p. 18) says, regarding Isotoma, "The clypeus, however, 

 is mero-ed with the epicranium, and the usual suture between them does 

 not appear distinctly in after life, though its place is seen in Figure 13 to 

 be indicated by a slight indentation. The labrum is distinctly defined 

 by a well-marked suture, and forms a squarish knot-like protuberance, and 

 in size is quite large compared to the clypeus. From this time begins 

 the process of degradation, when the insect assumes its Thysanurous 

 characters, which consist in an approach to the form of the Myriapodous 

 head, the front, or clypeal region being reduced to a minimum, and the 

 antennse and eyes brought in closer proximity to the mouth than in 

 other insects." 



Lemoine ('83, p. 510, Planche XV., Figure 24) mentions in Smynthu- 

 rus, " Les deux appendices qui constitueront la levre superieure," but 

 they appear in his figure as only simple lobes from a large, median 

 labrum . 



Wheeler ('93, p. 57, Figure VI.) represents the labrum of Anurida as 

 a median, unpaired fundament, and Claypole ('98, Plate XXIII.) gives 

 several surface views of the upper lip in the same species. 



Uzel ('98, Taf. VI., Figur 87) shows the single labral fundament of 

 Macrotoma (Tomocerus). 



Regarding Campodea, Uzel ('98, p. 26) says : " Yor der Mundeinsen- 

 kung erblickt man jetzfc schon die unpaare Anlage der Oberlippe," and 

 partially illustrates (Taf. IV., VI.) the development, which proceeds 

 essentially as in Anurida. 



The finished labra of Campodea (Grassi, '86'', Tav. IV., Figura 7) and 

 Japyx (Grassi, '86'', Tav. II., Figura 15 bis) are very simple rounded 

 plates. 



For Lepisma, Heymons ('97*, Taf. XXX.) figures the labral funda- 

 ment as a prolongation from the procephalic lobes, and characterizes it 

 (p. 591) as " eine kleine, voUkommen, ungetheilte, einfache Platte." 

 Later (p. 59.3) he says, " Die Oberlippe wird bedeutend grosser und 

 bekommt an ihrem hinteren Rande eine mediane Einkerbung (Figure 17)." 

 The median indentation is clearly, however, a secondary formation. 



In both Lepisma and Machilis (Oudemans, '88, Taf. I., Figur 3) the 

 labrum remains simply an anteriorly rounded plate. 



In the Orthopteran (Ecanthus, Ayers ('84, p. 240, Plate 18, Figures 

 21, 22) describes the unpaired fundament which forms the ovate labrum. 

 In short, the labrum in all Orthopteran families develops from an un- 

 paired fundament. (See Wheeler, '93, Heymons, '95^) 



The same is true of the Libellulidae and Ephemeridae (Heymons, '96, 



