78 Journal New York Entomological Society, t^'o'- ^^i-^. 



that, as we pass over into the insectan type, the basignath, or basai 

 region of the mandible included between the^ points " a," " b " and 

 " c," becomes somewhat slenderer and more elongate, and the outline 

 of the black -margined area from " a " to " c " is less sinuate. An 

 impressed line extending from "h" to "c" (compare also Fig. 5, 

 Plate VI) is continued around the other side of the mandible and 

 demarks the basal region, or basignath, from the distal portion of 

 the mandible, or the distignath. The secondary nature of this sub- 

 division of the mandible, is clearly evident if we trace back the evolu- 

 tion of the basal segment of the mandibular limb through the various 

 stages from textfigure 6 to textfigure i ; so that it should be patent to 

 anyone that the mandible of the insect shown in textfigure 6 repre- 

 sents a single segment of the original mandibular appendage, and any 

 attempt to compare the parts of an insect's mandible (which is com 

 posed of only one segment of a limb) with the parts of the "body" 

 of an insect's maxilla (which is composed of at least two segments 

 of a limb) is wholly unjustified. 



The incisor process of Machilis (i.e., the stippled region from 

 "d" to " e" in textfigure 6) is clearly the equivalent of the incisor 

 process of Apseitdes {i.e., the stippled region from "d" to " c" in 

 textfigure 5), and it is consequently merely a differentiated portion 

 of the masticatory region of the mandible of Mysis (i.e., the region 

 from "f" to "e" in textfigure 4) in no wise comparable to the 

 mandibular palpus " en " of textfigures 5, 4, 3, etc., as Heymons would 

 maintain is the case with the incisor process of immature Ephemerida, 

 nor can the incisor process of Machilis (i.e., the stippled area from 

 " d" to "e" in textfigure 6) be compared to the exopodite of a 

 biramous limb (i.e., "ex" of textfigure i) as Wood-Mason would 

 maintain is the case ! The lacinia mobilis "' li " and the gnathofim- 

 brium " g " of the mandible of the crustacean shown in textfigure 5, 

 are lost in the mandible of the insect shown in textfigure 6 ; but this 

 is not surprising, since these structures are frequently absent even in 

 the Crustacea themselves (e.g., in the crustacean mandible shown 

 in Fig. 6, Plate VI). The molar process "/" of the insect's mandible 

 shown in textfigure 6 is clearly homologous with the molar process 

 " f" of the crustacean's mandible shown in textfigures 5, 4, and 3, 

 and is consequently merely a ditterentiated portion of the masticatory 



