Chap. XL EVOLUTION. 121 



that approaching most nearly to the original one, is 

 easy to judge from the above statements. 



The jprimitive history of a species will he preserved in 

 its developnental history the more perfectly, the longer the 

 series of yowig states through which it passes hy uniform 

 steps ; and the more truly, the less the mode of life of the 

 young departs from that of the adults, and the less the 

 peculiarities of the individual young states can he con- 

 ceived as transferred hack from later ones in previous 

 periods of life, or as independently acquired. 



Let us apply this to the Crustacea. 



Crustacea are there forms "which might resemble the maggots of the 

 Diptera or Hymenoptera, the larvae of the Coleoptera, or the caterpillars 

 of the Lepidoptera, still less any bearing even a distant resemblance to 

 the quiescent pupse of these animals. The pupse, indeed, cannot at all 

 be regarded as members of an original developmental series, the 

 individual stages of which represent permanent ancestral states, for 

 an animal like the mouthless and footless pupa of the Silkworm, 

 enclosed by a thick cocoon, can never have formed the final, sexually 

 mature state of an Arthropod. 



In the development of the Insecta we never see new segments added 

 to those already present in the youngest larvae, but we do see segments 

 which were distinct in the larva afterwards become fused together or dis- 

 appear. Considering the parallelism which prevails throughout organic 

 nature between j^alseontological and embryonic development, it is there- 

 fore improbable that the oldest Insects should have possessed fewer 

 segments than some of their descendatits. But the larvse of the Cole- 

 optera, Lepidoptera, &c., never have more than nine abdominal segments, 

 it is therefore not probable that they represent the original young form 

 of the oldest Insects, and that the Orthoptera, with an abdomen of 

 eleven segments, should have been subsequently developed from them. 



Taking into consideration on the one hand these difficulties, and on 

 the other the arguments which indicate the Orthoptera as the order 

 most nearly approaching the primitive form, it is my opinion that the 

 "incomplete metamorphosis" of the Orthoptera is the primitive one, 

 inherited from the original parents of all Insects, and the "complete 

 metamorphosis" of the Coleoptera, Diptera, &c., a subsequently acquired 



