AND PHYSIOLOGY. 153 



m m 



mass of these animals is made up of the lateral muscles of 

 the body which extend from the head to the caudal fin ; and 

 as each ]ateral muscle by its contraction bends the body to its 

 own side, the motion of the fish through the water is effected 

 in the same manner as the oarsman sculls his boat. 



Fig. 163. 



Muscular Fiber from Leg of Meat Fly. a, Termination of Muscular Fiber, t, Tendon. 



285. Muscles and Locomotive Organs of the Inverte- 

 brates. — Muscles, both striated and smooth, voluntary and 

 organic, abound in all the invertebrates. They are modified 

 in form and position to meet the wants of the animal as wisely 

 as in the higher tribes. 164 - 



In some of the Polypi 

 movements are made by 

 the contraction of their 

 sides, in which no mus- 

 cular fibres have been 

 discovered, though ex- 

 existing in other parts 



of the animal. The Insect Fasciculi Magnified Fifty Diameters. 



muscles of insects are either colorless or of a dirty yellow. 



286. A great variety of locomotive organs are found in the 

 Invertebrates. The Echinoderms have tentacles, called Am- 

 bulacra, on some of which there are suckers, which enable 

 them to hold on to substances. They have also forcep-like 

 organs of locomotion. Most of the acephalous molluscs move 

 by a highly developed foot, which, in the Cephalopoda, is used 

 as a sucker. The Cephalopods have arms with suckers at- 



What portion of the body is made up of them? 286. What are the locomotive organa 

 of Invertebrates ? 



