62 THE ANIMAL KINGDOM. 



structure more nearly resemble the animal than the insect 

 eye. Sometimes there are eight, sometimes six, or only 

 two. They have a mouth with jaws (maxillte), a tongue 

 (ligula), remarkable palpi, and frontal claws often of great 

 magnitude. But the nervous system is the great distinction. 

 The organ of sensation, which is the brain in man and 

 animals, is a series of knotted nerves called ganglia in insects, 

 from which proceed nerves to all parts of the body. The 

 imperfect insect, such as a Caterpillar, has more ganglia 

 than the perfect butterfly. And whereas the insect has 

 generally from six to eight or ten ganglia, or little brains, 

 in different parts of its body, the spider has but two, and 

 they more brain-like, more concentrated, and consequently 

 of a higher order. 



Then again as to the circulation : we know that in all 

 creatures the blood is the life ; it is the fluid which nourishes 

 all parts of the body. Not always red; it may be white, 

 or yellow, or green ; but it is blood, and constituted more 

 or less like our human blood, as the microscope reveals. 

 All insects have a heart or dorsal vessel which pumps 

 out the blood (as we shall see explained when examining 

 the larvae of ephemera) that circulates loosely in the body, 

 bathing the air vessels which supply it with oxygen ; but the 

 Arachnida have a true heart ; long, indeed, like the insect 

 heart, but furnished with arteries and veins which give it 

 perfect circulation. This raises it another step higher. 



The respiratory system is different in various species; 

 but the Spider whose foot we are looking at had lungs or 

 pulmonary sacs, with two or four breathing orifices, situated 

 just near the base of the abdomen, and inside those sacs a 

 number of delicate white triangular plates which aerated 

 the blood. This is more like animal respiration than the 

 trachea of insects. (See Spiracles.) 



The Arachnida do not undergo metamorphosis. The 

 female lays eggs, making very pretty cocoons or nests for 

 them, and the young Spiders come forth perfect from the 

 shell, with the exception of the two fore legs, which are 

 not always developed until a few days after their birth. 



And if we read any good work on the Arachnida we 



