286 THE CANADIAN ENTOMOLOGIST 



bearing three pairs of "stumpy" legs in the abdominal region 

 with reduced terminal appendages, etc., etc., are "foreshadowed," 

 so to speak, in the BathyneUa type of Crustacea, in which the 

 body is also long and slender, and appears to be composed of 

 approximately twenty-one segments. In BathyneUa also, there is 

 a marked tendency toward the reduction (or shortening) of the 

 terminal appendages, and the last five segments of the body have 

 lost their limbs completely, while the hindmost legs exhibit a 

 marked tendency to become shortened and reduced — a condition 

 which, if carried a little further, would result in the production of 

 a creature in many respects quite similar to a proturan insect. 



On the other hand, the "Isopoda-Amphipoda'^ group of 

 Crustacea (including the Tanaidacea) exhibit many develop- 

 mental tendencies which find opportunity for expression in certain 

 other Apterygota. Thus the multiarticulate terminal appendages 

 of such forms as A pseud es are suggestive of the many-segmented, 

 paired cerci of such Apterygota as Lepisma, Machilis, etc., and the 

 nature of the limbs, head, mouth-parts, and other structures in 

 the Isopod-Amphipod group, is strongly suggestive of the con- 

 dition found in certain Apterygota, even in regard to the minuter 

 details. If we admit the possibility of the ancestors of insects 

 differing markedly among themselves (as there is every reason to 

 suppose was the case) it is, therefore, quite probable that some 

 of them resembled the anomostracan type of Crustacea, while 

 others probably resembled the isopod or amphipod type of 

 crustacean. 



It is quite probable that the ancestral "myriopods" were 

 similar in many respects to the members of the "Symphyla- 

 Pauropoda" group, and it would be a comparatively simple matter 

 to derive these types from crustacean forms allied to BathyneUa 

 or other Anomostraca. If we assume that both the apterygotan 

 type of insect and the Symphylo-Pauropodan type of "myriopod" 

 were derived from crustacean forms allied to those mentioned 

 above, it is evident that the myriopodan type in question has 

 followed a course of development very close to that of the lower 

 apterygotan insects; and in certain respects these "Myriopoda" 

 have departed less from the ancestral condition than the most 



