THE FLY. 55 



From this crop the food passes into an extended 

 stomach, and thence into a long convoluted bowel, to 

 which are attached Qumerons biliary tubes, and which 

 terminates in an expansion called the cloaca. This 

 complicated digestive apparatus extends throughout 

 the whole body, the throat commencing in the head, 

 and terminating in the thorax, in which is also situ- 

 ated the stomach and its appendages; whilst the 

 long winding intestine is found, along with the other 

 viscera, in the last or abdominal section of the body. 

 Instead, therefore, of a simple alimentary canal, pass- 

 ing in a straight line from end to end of the body, as 

 we found ia the Worm, the lowest of the articulate 

 series, we have here four distinct divisions in the di- 

 gestive apparatus, — a progressive step in the develop- 

 ment, with which we shall find the other vital organs 

 in perfect accordance. In regard to the circulation of 

 the blood, for instance, you will recollect that the 

 Worm possessed one undivided contractile tube, which 

 extended along the back, and, performing the func- 

 tions of the heart, propelled the vital fluid along the 

 whole body, after which it was again collected in 

 another canal running along the ventral portion of 

 the animal. Now in the Fly, although the principle 

 of operation is precisely the same, the organs that per- 

 form the function are far more highly developed. The 

 dorsal vessel (heart) extends along the whole body, 

 just within its external covering, and differs from 

 that of the Worm inasmuch as that portion of it 

 which is situated in the third or abdominal section of 



