128 ANIMAL PHYSIOLOGY. [LESSON 37. 



to procure a minute injection of a lobster, is to put a pipe into a claw 

 and pass the iDJection through it. The venus sinuses will fill first, 

 afterwards the arteries and the heart. 



587. If, in the ferocious combats to which the lobsters are always 

 exposed, one happen to wound a claw of its adversary, the injured 

 lobster instantly casts off the limb, always at a particular joint at 

 the second articulation. If this were not done, the animal would 

 soon bleed to death, in consequence of the lacerated venus sinus. 

 Cast off at the joint indicated, provision is made there, but nowhere 

 else, for the perfect contraction of all the soft parts, and, as the lob- 

 ster possesses the power of renewing lost portions of its structure, no 

 permanent injury results. 



588. The membranes composing the walls of these sinuses are of 

 such extreme tenuity, that they can only be demonstrated by the aid 

 of the injecting syringe ; the most careful and accurate, dissection 

 fails to discover them. 



LESSON XXXVII. 



ORGANS OF NUTRITION IN INSECTS. 



589. The intestinal canal of any animal is the tube which com- 

 mences at the mouth, and is devoted to the reception of nutriment, 

 whereby the growth and development of the individual may be pro- 

 moted, and the wear and tear, and positive loss since the last meal, 

 may be compensated for. In all the higher animals this canal pos- 

 sesses an opening at the opposite extremity ; that this is not essen- 

 tially necessary we have abundantly seen in relation to classes al- 

 ready discussed Infusoria; Entozoa ; many Polypi,- the Acale- 

 pha; and Asterias, amonst the Echinodermata. 



Examples of this condition are not wanting in Insects, but it 

 rarely occurs, and is only met with in the infantile condition (larvae, 

 maggots), and never in the perfect insect. 



590. This canal is subject to great modifications of distension 

 and constriction, whereby it is separated into a variable number of 

 divisions, and as the function of these divisions is dissimilar, they 

 have received different names. In addition to the partition of the 

 canal, there are peculiar processes, or appendages, which either origi- 

 nate from or open into it. 



