June, i9;:i.] CraMI'TOX : EvOI.L'TIOX OF THK A NTH KOl'ODA. 95 



velopment of the basal se.e^ment of the maudil)ular ai)j)endage to form 

 the body of the mandible proper, and the ditterentiation of the 

 masticatory surface of the gnathobase into an incisor and a molar 

 area. 



5. In the mandibles of the My>idacea and hijjher Crustacea, h 

 lacinia mobilis is formetl in the inci>or region {i.e., the region distal 

 to the molar process) through the fusion of several hair-like or spine- 

 like structures similar to those which form the so-called gnatho- 

 fimbrium or bordering fringe of the region of the mandible im- 

 mediately beyond (distal to) the molar process. These structures 

 also occur in the mandibles of insects, but the homologue of the 

 mandibular palpus of Crustacea has never been found in any insect 

 thus far described. 



6. The mandible of MacJiilis represents one type of insectan 

 mandible which is even more crustacean than insectan in appearance, 

 and the derivation of this type of mandible from a crustacean pre- 

 cursor involves so slight a change, that the evidence drawn from a 

 study of the mandibles is in full accord with that drawn from other 

 sources, which indicate that the Crustacea probably represent the 

 forms ancestral to insects. 



7. The character of the mandible of Macliilis indicates that it is a 

 very i)rimitive form, and the many crustacean features preserved by 

 Ma^hilis clearly indicate that it is a much more primitive insect than 

 it is generally supposed to be. This insect is anatomically annectant 

 between the Crustacea and such apterygotan insects as Lcf^lsnui. 

 Xicolctia, etc., which in turn lead to the lower types of winged insects 

 such as the Ephemerida, and through them and the Plecoptera to the 

 remainder of winged insects. There is no reason whatsoever for the 

 unfounded claim that Macliilis is a degenerate winged insect, and it 

 approaches the crustacean type so closely that if Macliilis is to be 

 regarded as a degenerate winged insect, then the Crustacea must also 

 be regarded as degenerate winged insects. 



8. It is utterly impossible to derive any insectan type of mandible 

 directly from the trilobitan tyjie of mandibular a])pen(lage, since the 

 immediate loss of the exopodite and the endopodite (which still func- 

 tions as a locomotor ajipendage in trilobites), the immediate assump- 

 tion of the mandibnlar form by the comparatively simple basa! segment 



