150 ANIMAL PHYSIOLOGY. [LESSON 43. 



669. The many digestive sacs of Locusta viridisima (large Eng- 

 lish grasshopper), and its allies, has its full representative in the four 

 digestive cavities of the herbivorous quadruped. The only great and 

 peculiar exception appears to be in relation to the pumping stomach 

 of the Lepidoptera, Hymenoptera, and Diptera, but even this, in 

 the opinion of some authors, but apparently with insufficient reason, 

 is met by the air-bladder of fishes. 



670. The persistency with which the glandular system is develop- 

 ed in insects, is no less remarkable. 



Salivary glands, to the extent of even three pairs, is by no means 

 uncommon, while few insects are entirely destitute of them. 



The Liver is almost always found, and usually extensively pro- 

 duced, while in its ultimate structure (cellular) it bears great affinity 

 with the same organ in higher animals. In none of the illustrations 

 produced was a kidney found, but this organ is by no means rare. 



Finally, in this class the most important problem, the ultimate 

 structure of glands, may be studied with great ease. In the higher 

 animals these organs are veiled by a parenchyma, which renders in- 

 vestigation difficult; but in insects, we find them already analyzed 

 existing as simple tubuli, and offering every facility for the most 

 minute examination of them. 



When the like organisms in man and the higher animals have 

 been successfully treated, and reduced to their elemental condition, 

 lo ! they too, are simple tubes ! 



LESSON XLIII. 



OEGANS OF NUTEITION IN ARACHNIDA. 



671. The general characteristics of this class have already been 

 given, together with the names of the orders into which it has been 

 divided. 



The Arachnidans are placed above the insects in the scale of 

 being for the following reasons : they present a more concentrated 

 condition of the nervous system, and of the heart ; and the larger 

 species possess a higher condition of the respiratory system, which is 

 not only less diffused than in insects, but in some of them consists of 

 air-sacs, or rudimental lungs. If a Spider be examined, it will be 

 seen at a glance that the head is confluent with the chest, forming 



