MULTICELLULAR ANIMALS 



241 



ness. The muscles (Fig. 166) of insects are considerably more power- 

 ful than those of vertebrates. They appear to be more gelatinous and 

 are colorless as compared with the vertebrate muscle, but they are 

 capable of great power and speed. We are told that if Man were 

 equipped with muscles equivalent to those of the grasshopper he 

 could jump many times as far as his best records; and that the 



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Fig. 167. — Human plain, cardiac, and striated muscle cells. Diagrammatic. Com- 

 pare the striated muscle cell with that of the insect muscle in Fig. i66. (Partly after 

 Kiihn: Griindriss der allgemeinen Zoologie, published by Georg Theime, Leipzig, 

 and partly after Shafer: Essentials of Histology, published by Longmans, Green and 

 Company.) 



wings of certain gnats beat 15,000 times a second. The high state 

 of functional efficiency of muscles in lower forms is understandable, 

 for it is as important for these animals to withdraw from danger or 

 move from place to place as it is for vertebrates. 



Vertebrate muscle cells are of three sorts, smooth cells forming 

 the muscular elements of the digestive and reproductive systems and 

 the walls of the arteries; cardiac muscle cells, confined to heart 

 muscle; striated or striped muscle cells, forming the large muscles 

 attached to the skeleton. The accompanying figures show the dif- 



