400 ENTOMOLOGICAL NEWS. [Nov.,'17 



intervenes between the coxa and the true pleural sclerites ; but 

 the remainder of the prothoracic sclerites of the Lepismids are 

 somewhat different from the typical sclerites of the lower 

 I'terygotan forms. In this respect, Nicoletia would have been 

 a better insect than Lcpisma for a comparative study of the 

 thoracic region, but I have hesitated to spoil my only specimen 

 of Nicoletia by subjecting it to the staining process with nitrate 

 of silver, etc., which is necessary to differentiate the sclerites 

 from the membrane in these weakly pigmented forms. 



There are two principal types of head found among the 

 Apterygotan insects, namely the broad, flattened type, occurr- 

 ing among certain Lepismids, etc., and the more pear-shaped 

 type, occurring in Japyx, etc. I find these two types repre- 

 sented among the Myriopods (sensu lato) and also among the 

 Crustacea, so that these two types were apparently differenti- 

 ated at a very early stage of development, and both were 

 doubtless present among the first insects to be evolved. In 

 fact. I believe that flat, broad-bodied forms as well as the 

 more cylindrical, slender-bodied forms occurred among the 

 ancestral insects (for such types also occur among the Crus- 

 tacea, etc.), so that it is incorrect to say that the original in- 

 sects were of this or that type, since several types must have 

 been in existence at the very beginning of the development of 

 insects. It is thus evident that insects are not the product of 

 one type of ancestral forms alone, but the ancestral insects 

 doubtless differed as much (if not more) among themselves 

 as the modern representatives of the different families compos- 

 ing an order of insects differ among themselves. 



It is undoubtedly true that throughout the animal kingdom, 

 many living forms have departed but little from the ancestral 

 condition characteristic of the early stages in the development 

 of other living groups, and are fully as instructive as fossil 

 forms are, in furnishing us with connecting links between many 

 of the greater groups of the animal kingdom (such, for 

 example, as the living Dipnoi, which furnish us with inter- 

 mediate forms annectent between the fishes and Amphibia). 

 In the same way, certain living insects have departed but little 



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