72 



lie. The sum total of tlie characters of the order indicate 

 that they are more closely allied to the Thysanura than to 

 any other order of Insecta, but that they also possess certain 

 generalised features in common with the lower Arthropoda. 



The CoUemhola are allied to the Thysanura in that 

 they are the only two orders of Insecta which possess an 

 evident pair of mouth-parts — the maxillulee, which are 

 intercalated between the mandibles and first maxillse. 

 They further resemble the Thysanura in the absence of 

 any traces of wings, and in the fact that they undergo no 

 metamorphoses. It is with the genus Campodea that 

 their affinities come closest, and they resemble that genus 

 in their mouth-parts being withdrawn into the head 

 capsule, in the ovaries consisting of a single tube on 

 either side, there being no ovarioles, and in the absence 

 of an amnion and serosa in the embryo. 



The Thysanura have been divided by Glrassi into two 

 divisions, viz., the Entotrophi, including the genera 

 Campodea and Japy.r, and the Ectotrophi, which com- 

 prise Machilis and hephma. The Entotrophi, as their 

 name implies, have their mouth-parts retracted within 

 the head, and it is true that they are more closely related 

 to the Collembola than is the case with the Ectotrophi. 

 The relationship, however, is not sufficiently close to 

 warrant the Collembola being included as a sub-division 

 of the Entotrojihi, as has been suggested by Stummer- 

 Traunfels (24). The difference in the number of segments 

 to the abdomen in the two groups presents a serious 

 difficulty to any such system of classification. It is by 

 no means certain that the entognathous condition of the 

 Collembola and Entotrophi is anything more than a 

 parallelism in evolution and, if that be so, it would be of 

 little value as a character implying a close relationship 

 between those two groups. 



