166 



THE AMERICAN NATURALIST [Vol. LIU 



therefore considered sucli lowly organized Apterygota as 

 Eosentomon, Anajapyx, etc., instead of the highly special- 

 ized Anurida, Sminthurns, etc., I am sure that his opinion 

 of the "degenerate" condition of the Apterygota as com- 

 pared with the Pterygota would have been quite the 

 opposite of that expressed in his paper. Furthermore, 

 there are practically no arthropods known which are 

 primitive in all respects, and, as is the case throughout 

 the whole realm of zoology, forms which have retained 

 many features in an exceedingly primitive condition may 

 be very highly specialized in other respects ; so that one 

 must take into consideration the composite primitive 

 features of the group as a whole ; and, just as the most 

 primitive members of the Pterygota are studied in an 

 attempt to determine their ancestry, so the most primi- 

 tive members of the Apterygota must be considered in 

 such a phylogenetic study. 



Even in the matter of the nature of their eyes, such 

 forms as MachiUs (which are related to Lepisma) can 

 hardly be called '^degenerate," and in the face of the 

 fact that in the trilobites themselves there occur at least 

 three types of eyes— ''isolated eyes or ocelli, aggregate 

 eyes of biconvex lenses, and compound eyes" (Tothill, 

 p. 321, quoted from Lindstrom, 1901), it is very improb- 

 able that the type of eyes found in Lepisma are of a 

 higher type than the compound eyes of the Pterygota. 

 As far as their mouth parts are concerned, I find the 

 lepismids much more primitive than the Pterygota (with 

 the possible exception of nymphal ephemerids) and Boer- 

 ner, 1908-1909, has called attention to crustacean struc- 

 tures so similar to those found in the maxilla, etc., of 

 apterygotan insects, that there can be no doubt that the 

 mouth parts of the Apterygota in general instead of 

 being "degenerate" have retained many more primitive 

 features than those of most lower Pterygota. 



As far as the number of abdoitiiiial sconK^nts is con- 

 cerned, some Apterygota, instead of having- fewer seg- 

 ments, have even retained twelve, and in these forms, 

 such as the Protura, there is also a postembryonic in- 



