404 



THE LANCELET 



and a hepatic portal system ; usually two pairs of limbs, and 



never more than two pairs ; and a series of body-muscles 



^„ which are divided into segments 



or myomeres (p. 203), at any rate in 



early stages. 







^-^ 



'M 



Now in various parts of the 

 world, occurring only rarely off the 

 English coasts, certain small fish- 

 like animals called lancelets are 

 found, the commonest species of 

 which is known as Amphioxus 

 lanceolatus (Fig. 98). This animal, 

 which possesses a median fin like 

 that of the tadpole (p. 207), is not 

 more than a couple of inches in 

 length, and lives in the sea near the 

 shore, burrowing in the sand ; it is 

 especially interesting owing to the 

 fact that it presents certain charac- 

 teristics indicating a near relation- 

 ship to the primitive ancestors of 

 Vertebrates. It possesses a noto- 

 chord, a dorsal hollow nervous 

 system, a pharynx perforated by 

 gill-slits, a hollow outgrowth of the 

 intestine representing a simple 

 liver, with a hepatic portal system, 

 " and a series of nephridia. But 



it differs from all the higher Vertebrates in the following 



important points. 



"' The epiderm consists of a single layer of cells. There 



is no distinct head and no skull ; the persistent noto 



d 





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