PROC. ENT. SOC. WASH., VOL. 24, NO. 2, MAR., 1922 71 



becomes more elongate. in Fig. 12, and its endite be becomes 

 differentiated into several lacinial structures which will be dis- 

 cussed later. The third segment or palpifer ip of Fig. 12 

 becomes more closely applied to the second segment bp and its 

 endite, the galea ie is proportionately much larger in Fig. 12 

 than in Fig. 11. The maxillary palpus en of Fig. 11 consists of 

 only four segments, as was mentioned above, while the palpus 

 en of the maxilla of Machilis shown in Fig. 12 is composed of 

 seven segments. It is also a simple matter to compare the 

 parts of the maxilla shown in Fig. 11 with those of the maxilla 

 of the primitive apterygotan insect Eosentomon shown in Fig. 

 17, since the basal segment cp of Fig. 11 evidently corresponds 

 to the small basal segment cp of Fig. 17, while the second seg- 

 ment bp of Fig. 11, with its endite be, evidently corresponds to 

 the second segment bp of Fig. 17, which also bears an endite be, 

 although the endite be of Fig. 17 has become differentiated into 

 certain lacinial structures not present in the endite be of Fig. 1 1 . 

 The third segment ip of Fig. 17 with its endite ie clearly corres- 

 ponds to the third segment ip with its endite ie of Fig. 11, and 

 there are indications of four segments in the maxillary plapus 

 en of Fig. 17 suggestive of the four-segmented maxillary palpus 

 en of Fig. 11. It is a simple matter to compare the maxillae of 

 higher insects, such as the one shown in Fig. 18, with the type 

 of maxilla shown in Fig. 12, and one may easily compare the 

 parts of the maxilla of an apterygotan insect, such as the one 

 shown in Fig. 17, with the type of maxilla shown in Figs. 16, 

 14, 9, etc., so that, having established the meaning of the parts 

 of the maxilla in one case, it is a comparatively easy matter to 

 apply the knowledge thus gained, to insects in general. 



In order that there may be no misunderstanding in this mat- 

 ter, I would call attention to the fact that in comparing the 

 parts of Fig. 10 with those of Fig. 11,1 have compared the parts 

 of a maxilliped of a crustacean with the parts of an insect's 

 maxilla, instead of comparing a crustacean maxilla with an 

 insect's maxilla. This however is perfectly justifiable, since 

 the segments of a crustacean's maxilliped are in every way 

 homologous (serially) with the segments of a crustacean's 

 maxilla and may be compared part by part, just as the protho- 

 racic leg is in every way serially homologous with a metathoracic 

 leg in an insect, and the prothoracic coxa, trochanter, femur, 

 etc., correspond in every way to the metathoracic coxa, tro- 

 chanter, femur, etc. Since the parts of the maxilliped are 

 homologous with those of the maxilla in Crustacea, it is there- 

 fore justifiable to homologize the parts of a crustacean's raaxilli- 

 ped with the parts of an insect's maxilla in an attempt to deter- 

 mine the proper interpretation of the insect's parts, it the maxil- 

 liped serves the purpose better than the maxilla does, as is the 

 case with those Crustacea available to me at present (although 



