DEFINITION OF THE TERM INSECT. 23 



approach to such structure may be traced in some Hexa- 

 pods ; for instance, the coalition of the head and trunk 

 in Melophagus, Latr., and that of the trunk and abdomen 

 in Sminthurus, Latr. a The Myriapoda exhibit other re- 

 markable diiferences ; though their head and trunk are 

 distinct, the former antenniferous, and their body annu-< 

 lose, the abdomen as well as the trunk is furnished with 

 legs, sometimes amounting to hundreds ; but even to this 

 a tendency has been observed in some Hexapods b . If 

 you examine a specimen of Machilis polypoda, an insect 

 related to the common sugar-louse (Lepisma saccharina)* 

 you will find that the abdomen is furnished with a double 

 series of elastic appendages, which, being instruments of 

 motion, may be regarded as representing legs. It is 

 worthy of notice, that the Myriapoda when first disclosed 

 from the egg have never more than six legs c , and keep 

 acquiring additional pairs of them and additional seg- 

 ments to their abdomen as they change their skins : and 

 it is equally remarkable, that many Hexapods are subject 

 to a law in some degree the very reverse of this, having 

 many abdominal legs in their first state, and losing them 

 all in their last. The union of the head with the trunk 

 in the Trachean Arachnida has been regarded as almost 

 an unanswerable argument, in spite of their different in- 

 ternal organization, for including them in the same class 

 with the Pidmonary Arachnida ; but the case of Galeodes, 

 which, though furnished with gills, (as an eminent Rus- 

 sian Entomologist Dr. G. Fischer is reported to have 

 discovered,) implying also a circulation, and evidently 

 belonging to the last-mentioned class, has nevertheless a 

 distinct thorax consisting of more than one piece, to which 



a De Geer, vii. t. iii./. 8. b Hor. Entomolog. 35' 



c De Geer, Ibid. 571, 583. t. xxxvi./, 20, 21. 



