284 ELEMENTARY BIOLOGY. [CHAPJ 



backwards and downwards, terminates to the lefq 

 of the respiratory orifice. 



e. The pericardium^ a small sac lying in a recess oi 

 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 orgai 

 and pericardium, and remove so much of them ag 

 remains, together with a portion of the adjacent 

 visceral sac. Wash carefully until clear of sediment 

 and examine in water under a low power. 



A short ciliated duct will be found, passing froi 

 the base of the pericardium to the excretory gland, 

 into which it opens by a retio-pericardial 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 anc 

 liberate the rectum from its surroundings. Next dis 

 sect away the right half of the body wall and viscera 

 sac. 



There will be seen filling up the greater part of the 

 body cavity the dead-white generative organs; re^ 

 move these en masse, whereupon there will be clearlj 

 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. 



I 



