90 Journal Xew York Entomological Society. L^'o'- X-^ix. 



of the Tanaidacea. Isopoda and Amphipoda as any, and it is more 

 logical to group them with these forms than to place them lower in 

 the scale of development than the ]\Iysidacea, as was formerly done 

 by the earlier carcinologists. 



The mandibles of the Isopoda (Figs, i and 36) and Tanaidacea 

 (Fig. 3) are remarkably similar, and both are very like those of 

 the Amphipoda (Fig. 4), and the resemblance on the part of the 

 mandibles thus further substantiates the evidence of a very close 

 relationship between these groups drawn from other sources. All of 

 these groups are apparently closely related to insects, and with the 

 exception of the presence of the mandibular palpus, the types of 

 mandibles occurring in these forms are approached by the mandibles 

 of certain insects some of which are members of even so high a 

 group as the Pterygota. It would thus appear that certain hereditary 

 impulses from the Crustacea have surged upward, so to speak, through 

 the apterygotan lines of descent and have penetrated well into the 

 lines, of descent of the pterygotan insects before losing their force 

 and becoming so greatly modified as to be no longer recognizable as 

 crustacean features. 



It should be borne in mind, that there are several types of 

 mandibles present in insects, which can be traced back to crustacean 

 types, and the type of mandible shown in textfigure 6 (which was 

 probably derived from the crustacean type shown in textfigure 5) is 

 only one of these. The type of insectan mandible shown in text- 

 figure 6, however, is so much like that of the crustacean shown in 

 textfigure 5, that it is almost more crustacean than it is insectan, 

 despite the fact that the insect (Mocliilis) to which it belongs, is in- 

 disputably an '' out-and-out " hexapod. The character of the head 

 and its appendages (Maxillary palpus, etc.) in Machilh, the nature 

 of its body, and many other features than its mandibles alone, pro- 

 claim its close relationship to the Crustacea; and if MachiUs is noth- 

 ing but a degenerate winged insect (instead of being a very primitive 

 type near the ancestors of winged insects) as Handlirsch, 1909, would 

 have us believe, then the Crustacea, to which MachiUs is so closely 

 related, must also be regarded as degenerate winged insects ( !) be- 

 cause MachiUs is anatomically much nearer the Crustacea than' 

 winged insects are — and if this be a sign of degeneracy, then the 

 Crustacea must be degenerate winged insects also. 



