2S-|. ELEMENTARY BIOLOGY. [CIIAP. 



backwards and downwards, terminates to the left 

 of the respiratory orifice. 



c. The pericardium^ a small sac lying in a recess of 

 the left hand border of the excretory gland. Re- 

 move its front wall and examine the heart ; it is 

 subdivided into a single auricle and ventricle. 



2. Cut away the upper part of both the excretory organ 

 and pericardium, and remove so much of them as 

 remains, together with a portion of the adjacent 

 visceral sac. AVash carefully until clear of sediment, 

 and examine in water under a low power. 



A short ciliated duct will be found, passing from 

 the base of the pericardium to the excretory gland, 

 into which it opens by a rcno-pcricardial aperture. 



D. The alimentary organs. 



I. Place the animal on its left side, and pin it down 

 through the muscular foot. Remove the lung-sac and 

 liberate the rectum from its surroundings. Next dis- 

 sect away the right half of the body wall and visceral 

 sac. 



There will be seen filling up the greater part of the 

 body cavity the dead-white generative organs ; re- 

 move these en ?/iasse, whereupon there will be clearly 

 visible — 



a. The crop ; a large sac-like organ, filling a con- 

 siderable portion of the body cavity. It is generally 

 rendered the more conspicuous on account of the 

 yellow colour of its contents. Its lining membrane 

 is thrown into a series of longitudinal folds; these 

 are visible through its thin walls, giving it an 

 apparent longitudinal striation. 



