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Proceedings of the Royal Irish Academy, 



and its existence is still ignored by most writers upon Arthropod 

 morphology. Its discovery is due to Hansen ('93), who points out 

 that the paired structures associated with the tongue in the Thysanura 

 and Collembola, and vaguely called " paragiossse " by most students 

 of those insects, are in reality a pair of jaws situate between the 

 mandibles and the first maxillae. He gives to them the appropriate 

 name of " maxillulse." It is strange that so important an observation 

 should have been received with marked neglect for many years, but 

 Howes ('02) has now accepted Hansen's interpretation. A careful 

 examination of these maxillulae in the Thysanuran, Machilis mariti^na, 

 must convince anyone that there is no escape from Hansen's conclusion. 

 If the mouth-parts are viewed in their natural positions, the tips of 



Fig. 2 



Fig. 1. Right Maxillula of MacMli maritima. x90. ga., galea; la., lacinia ; 

 pip., palp. 

 2. TuBitM.B.^lnia. oi Isotoma palustris. x 260. ga., galea ; la., lacinia. 



the maxillulae are seen to lie just behind the mandibles, and in front 

 of the maxilla ; while, when dissected out, these organs show all the 

 appearance of a reduced pair of jaws (fig. 1 ). On the outer edge of each 

 maxiUula is a short vestigial palp ; while the tip of the appendage has 

 two very distinct lobes, corresponding with the galea and lacinia of 

 a typical maxilla. Both lobes show a beautiful arrangement of 

 spicules, ridges, and pits ; and the lacinia, at least, is jointed with the 

 basal sclerite. The maxiUuIae, at their bases, articulate with the central 

 tongue. In Japyx these organs are still more highly developed, with 

 three-segmented palps, according to Hansen ('93). 



