Chap. 14 



THE BY-PRODUCTS OF METABOLISM EXCRETION 



245 



Intestine 



Body cavity 



ynx 



rst aortic 

 h (heart) 



Kidney 



Hea 



Internal openings 



A. EARTHWORM 



Coiled tube 



entwined with 



capillaries. 



(latter not shown) 



External opening 



B. CRAYFISH 



^^ 



Detail 

 of one' 

 Kidney 



Mid gut 



Kidney (Molpighian) 



Hind gut 



Anal 

 opening 



C. INSECT 



Anal 

 ^ opening 

 f Blood 



Fig. 14.2. Examples of the tubular structure of excretory organs and their 

 characteristic association with body fluids. A, left. Earthworm: body cavity and 

 first pair of kidneys seen from the dorsal side; there is one pair in each of the 

 one hundred or more segments behind this. Right, Body cavity of earthworm 

 seen from the side showing one of each pair of kidneys; the inner end opens into 

 the body fluid; the coiled tube is entwined with blood capillaries. B, Left kidney 

 of the single pair of kidneys in the crayfish seen from the side after the shell 

 and gills are removed. It appears as two bodies, one including the bladder and 

 another called the "green gland." The gland consists of a labyrinth of excretory 

 tubules connecting through a canal with the urinary bladder which has an ex- 

 ternal opening just below the eye. Blood capillaries are entwined about the tubules. 

 The entire crustacean kidney has been compared to one unit of the vertebrate 

 kidney. C, Simplified diagram of an insect's body cavity and organs. The kidneys 

 (Malpighian tubes) open into the gut and extend into the body cavity where they 

 are continually bathed by the blood. (A redrawn from Strausbaugh and Weimer: 

 General Biology. New York, J. Wiley and Sons, 1944.) 



