LABORATORY EXERCISES I 27 



(c) In a small living snail the movement of the heart may be seen 

 through the shell. 



(d) When the shell is removed the lung chamber may be laid open. 

 Note also the heart, kidney, liver, coils of the intestine and, at 

 the top of the spiral mass, the gonad. 



(e) If the dorsal body wall is removed from the tentacle to the heart 

 the following organs come to view: The buccal mass, the oes- 

 phagus surrounded by the nerve collar, the crop with the sali- 

 vary glands at either side, the complicated reproductive organs 

 lying on the right side of the body. 



(f) Draw a dorsal view of a clam. Note the symmetry. (The 

 hinge is dorsal and the siphon posterior.) 



(g) The clam may be studied with one valve of the shell removed. 

 Note: The mantle, the two adductor muscles and the siphon 

 with its two openings. At the dorsal edge of the mantle is the 

 pericardial cavity in which lies the heart. 



(h) Raise the mantle and observe the large chamber in which lie 

 the visceral mass and the fleshy foot. Upon the visceral mass 

 lie the two gills and at the anterior edge the palps which hide 

 the mouth. 



(i) Draw a lateral view of a squid. Note the head with the arms 

 and eyes. Behind the head are the collar and funnel. The 

 body is covered with a very thick mantle which is expanded 

 at the end into a fin. 



(j) Study the suckers on the arms. Find the mouth and jaws. 



(k) The visceral mass and the gills are exposed by slitting open the 

 mantle on the ventral side. 



(1) The rudimentary shell is embedded in the dorsal surface of the 

 mantle. 



INTRODUCTION 



302. Animals and Plants. — Animals present a much greater 

 variety of types of organization than plants. This is largely 

 because the higher animals are vastly more complex Ihan the 

 higher plants. The apparent complexity of a tree, for exami)le, 

 is in reahty due chiefly to a repetition of similar parts; but in 

 animals there is a progressive differentiation of parts from the 

 lowest to the highest forms, so that even a single cell may have 



