folsom: mouth-paets of anukida maritima. 103 



end continues to bend toward the median plane until the apices of both 

 mandibles meet. The terminal unicellular lobes become multicellular and 

 secrete the incisive teeth (Plate 6, Figure 37 de. ids.), of which there are 

 finally five principal ones on the right and six on the left mandible. 

 Although the " head " of the completed organ is almost solid chitin 

 (Plate 6, Figure 37), there are five canals, one penetrating the base of 

 each tooth ; the hypodermal cells have, however, receded from the 

 « head." 



The extreme basal end of the finished mandible is prolonged as a 

 chitinous, conical projection (Plate 6, Figure 36, cdoc.)^ which, as in 

 Orchesella, is let into a concave chitinous piece that I have called the 

 stirrup {sta.), from which it may be withdrawn when tlie mandibles are 

 protruded. This projection, or pivot, arises in Stage 7 (Plate 5, Figure 

 32, cdx.) as a hypodermal evagination of the mandibular fundament, and 

 simultaneously the chitinous stirrup {sta.) is formed in a transverse, 

 superficial groove of the hypodermis lining the pharyngeal pocket in 

 which the mandible lies. In Orchesella the lateral end of the stirrup 

 unites with the external cuticula of the skull after traversing two layers 

 of hypodermis : first, the layer lining the mandibular pocket, and 

 second, the superficial layer of the head ; in Anurida, however, I have 

 found no such union between stirrup and skull. The body of the man- 

 dible is simply a modified cone, and hence in sections across this region 

 appears as a complete chitinous ring (Plate 7, Figures 44, 45, md.). 



In Anurida no trace of a mandibular palpus exists at any stage, and, 

 unlike Orchesella, no molar surface is differentiated ; the latter fact is 

 correlated with the character of the food : Orchesella feeds upon ligni- 

 fied vegetable substances, Anurida upon the soft tissues of the mollusk 

 Littorina littoria. In further correlation with diet, the powerful rota- 

 tors, or grinding muscles, of Orchesella are not represented in Anurida. 



Several writers on Collembola have already given surface views of the 

 mandibular fundaments at early stages, although none have traced their 

 development. I refer especially to Lemoine ('83, Smynthurus) and 

 Wheeler ('93, p. 57, Figure VI., Anurida). Packard ('71, p. 17 ; 

 Plate 3, Figure 13) evidently overlooked the mandibular fundaments of 

 Isotoraa, and what he regarded as mandibles are clearly, from their 

 position, the first maxillee. Ryder ('86) made the same mistake. 



Claypole ('98, Plate XXIII.) gives several figures of the mandibular 

 fundaments of Anurida maritima before much differentiation has oc- 

 curred, and Uzel ('98, Taf. VI., Figur 87) represents the fundaments 

 in Macrotoma (Tomocerus) at a stage equivalent to that of my Figure 



