402 



THYSANURA, 



CASE in the same order, and consequerxtly broke it up and made two 

 orders of it — one, the Spring tails, which he called Co'llembola, 

 and the other the Lepismid^, for which he retained the name 

 Thysanura. No one can dispute that there is a marked distinc- 

 tion between the two — the one with its jumping apparatus, and 

 the other with its projecting terminal, jointed bristles, besides 

 other distinguishing characters — and effect must be given to these 

 differences in some shape ; but whether it is sufficient to warrant 

 the establishment of two orders seems doubtful. This is not the 

 place to go into a discussion as to the value of the differences and 

 resemblances, but we may point to one that, although trifling in 

 Itself, seems to us very suggestive. It is the identity in type of 

 the peculiar scales with which they are clothed, and which are 

 common to, although not universal in, both sections, and are met 

 with in no other order of insects. These scales have another and 

 an economic interest for us : they have for long been employed as 

 tests for the quality of object-glasses of the microscope, from the 

 facility with which they display both the spherical and chromatic 

 aberrations. The woodcuts show the scale of Tomocerus (one of 



Scale of Tomocerus longicornis, much magnified, 

 and portion of it still more enlarged. 



Scale of Machilis, mucn mag'nified, and portion of 

 it still more enlarged. 



the Collembola) and that of Machilis (one of the Lepismidae — 

 Lubbock's Thysanura), and it will be seen that the type is the 

 same in both. We also show the more common form of the scale 



