STRUCTURE OF INSECTS. 2^1 



have a peculiar modification of the organs of respiration and 

 circulation. A current of water is constantly passed over 

 the gills by the action of the mouth of the animal, and by 

 means of the air it contains, exerts an influence over the 

 blood circulating in them, and produces the same changes 

 in it as are produced in the lungs of other animals by the air 

 they breathe. A few fishes, one of which is called the tor- 

 pedo, are possessed of a very remarkable means of defence, 

 which consists in the power of inflicting upon whatever liv- 

 ing creature comes in contact with them, a powerful elec- 

 trical shock. These shocks are so powerful, that in South 

 America, horses driven into the pools which some fishes of 

 this kind inhabit, have sometimes been stunned and even 

 killed. The shocks become weaker and weaker upon con- 

 tinued repetition, till the animal is exhausted, and loses for 

 some time the power of producing any effect. 



Questions. — 1. What is said of reptiles? 2.- Describe the first 

 order. 3. The second. 4. The third. 5. The fourth. 6. Describe 

 tlie organs of respiration and circulation in fishes. 7. What remark- 

 able means of defence have some fishes ^ [Note. Fishes are divided 

 into orders and genera, according to certain diflerences in the forma- 

 tion, structure, and situation of their mouth, gills, gill-coverings, fins, 

 &c. : — and they are called Apodes, as eels,; Jugulares, as cod ; Tho- 

 racici, as perch ; Mdominalcs, as pike and salmon.] 



LESSON 99. 



Structure and Transformation of Insects. 



Faucet a little face or side of a body cut into a number of angles. 

 Hexag onal, having six sides, or angles. 



Lu'bricated, made smooth so as easily to glide over any part. 

 Entomology, that branch of natural history which treats of insects. 



The animals of this class are remarkable for a greater 

 variety of powers and a more wonderful display of instinct 

 and intelligence, than any other of the invertebral animals. 

 They are distinguished by many peculiarities of form. In- 

 stead of a heart, insects have a vessel or reservoir situated 

 along the back, extending from one end of their bodies to 

 the other, and filled with a transparent fluid, which is sup- 

 posed to answer the purpose of blood, and to be conveyed, 

 by absorption, to the various organs. They have no parti- 

 19* 



