152 



INVEETEBEATE ANIMALS. 



juices of their prey. The intestinal canal is usually short and 

 straight, and is continued without convolutions to the aperture of 

 the anus. Salivary glands are also present, as well as ramified tubes 

 (" Malpighian tubes ") which are believed to act as kidneys. 



The circulation is maintained by means of a dorsal heart, which 

 is situated above the alimentary canal. The typical Arachnida 



101. — Pedipalpi. A, Scorpio afer, viewed from above, and somewhat reduced in 

 .size. B, Front jtortiou of the head of the same, viewed fi-om above, and enlarged. 

 C, Bulhiis Kocliii, with the terminal segments and the ends of the appendages on 

 one side omitted, m M.axillary palpi (behind these are the four pair of ambula- 

 titry legs); c Clieliceraa ; t Telson : o Lateral ocelli; o' Central, larger ocelli; g 

 Opercular plate, cohering the opening of the reproductive organs ; r One of the 

 " combs ; " s One of the openings into the pulmonary sacs. (C is after Prof. Ray 

 Lankester.) 



breathe air directly, and the function of respiration is performed by 

 the general surface of the body (as in the lowest members of the 

 cl;i.ss), or by bi;inched air-tubes termed "tracheae," or by distinct 

 pulraonai-y chambers or sacs, or, lastly, by a combination of tracheae 

 with pulmonary sacs. The trachea; are essentially similar in sti'uc- 



