8 STRUCTURE. 



the tliousand-lecjged worms, the centipede, the oar-wig, 

 and the Ll^e. 



2 J. The Araclinida^ having tight legs, and the head 

 and thorax joined together, while the abdomen is usually 

 distinct, comprising such as the spiders, ticks, mites and 

 scorpions; and 



3d. The Insects^ which are distinguished in their per- 

 fect or adult condition, by having tliree distinct ^)«/'?6' of 

 the body — head, thorax and abdomen — and having always 

 six legs on the thorax. 



The study of Insects comprises three departments : 



1st. The Traxsfohmations of Insects, and their struc- 

 ture in each of the stages through which they pass. 



2d. The Classification of Insects into Sub-Ordeks, 

 ^Families, Genee.v and Species, and 



3d. The Na:ukal Histoez of these several groups, surh 

 as the appearances, habits, associations, geographical dis- 

 tribution, etc. 



The first two of these departments alone will be outlined 

 in this printed text, while tlie third, and by far the most 

 interesting and important department, will be left for the 

 Lecture Eoom. 



1. Transformations. — Insects pass through four stages 

 in their development, i. e. : 

 1st. The Ejrcr, 



2d. The Larva, 



3d. The Pupa, 



4tli. The Imago, or Adult Insect. 



