FOLSOM: MOUTH-PARTS OF ANURIDA 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. 7’cvs.), of which there are 
finally five principal ones on the right and six on the left mandible. 
Althongh 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, cdz.), 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stirrup (sta.), from which it may be withdrawn when the mandibles are 
protruded. This projection, or pivot, arises in Stage 7 (Plate 5, Figure 
32, edz.) as a hypodermal evagiuation 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 
Isotoma, and what he regarded as mandibles are clearly, from their 
position, the first maxilla. 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 
