GENERAL REMARKS. 285 



age, having replaced or driven out the ancestral, prim- 

 itive, perhaps Thysanuriform mouth parts from the lar- 

 val stage. The assumption that the sucking mouth parts 

 originated in the pupal or adult stages is considered 

 probable, because, although there are many exceptions, 

 characteristics usually originate in the later stages in 

 other branches of the animal kingdom. In Lepidop- 

 tera and Diptera, which resemble the Hemiptera in 

 having the highly modified mouth parts with a tubular 

 arrangement, these characteristic peculiarities are con- 

 fined to the later stages of development, and are not 

 found in their larvae. The larvae of Hemiptera are 

 also decidedly Thysanuriform, and that they origi- 

 nated from a modified Thysanuroid form having bit- 

 ing mouth parts in the larvae and sucking mouth parts 

 in the later stages, seems to be indicated by this fact. 

 We have already seen in such examples as the locusts, 

 etc., that an earlier development in the inheritance of 

 the characters of adults may effectually obliterate the 

 Thysanuriform larva, and in the Coleoptera, Neurop- 

 tera, etc., that it is the earlier inheritance of the sec- 

 ondary larval characteristic which accomplishes this 

 result. In no case do the pupal or adult character- 

 istics become accelerated in development so as to 

 replace the larval stage in the second series of orders 

 except in parasites such as the parasitic Pupipara 

 (ticks). The young are in some of these species born 

 as pupae, and the ovarian and larval stages are passed 

 within the mother.' 



1 Among the orders having the direct mode of development 

 a similar case to the Pupipara is ta be found in the plant-lice. 

 These being viviparous, the young are born in an advanced 



