404 



THE LANCELET 



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



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



whieh are divided into segments 



A S Si= or myomeres (p. 203), at any rate in 



i" i.' early stages. 



;r 



.''. Now in various parts of the 



1 5 world, occurring only rarely off the 



■-5 J English coasts, certain small fish- 



V^ like animals called lancelets are 



■'I found, the commonest species of 



.", tj \vhich is known as Amphioxus 



fe S laitceolatus (Fig. 98). This animal, 



2^ which possesses a median fin like 



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



~f more than a couple of inches in 



Vh length, and lives in the sea near the 



\-i shore, burrowing in the sand ; it is 



i'^ especially interesting owing to the 



sl fact that it presents certain charac- 



? ; teristies indicating a near relation- 



s 5 ship to the primitive ancestors of 



I'f Vertebrates. It possesses a noto- 



|S chord, a dorsal hollow nervous 



<' system, a pharynx perforated by 



- '^ gill-slits, a hollow outgrowth of the 



^)'''/\"j; i-^ .S intestine rejjresenting a simple 



S j: |,= liver, with a hepatic portal system, 



^ and a series of nephridia. But 



it differs frmn all the higher Vertebrates in the following 



important [joints. 



' 'J"hc ejiiderm r(;nsists ol a single layer of 1 ells. There 

 is no distinct head and no skull ; the persistent noto 





