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"back and tail fin, but possesses none of the " paired " 

 fins, which, existent in most other fishes, represent 

 the limbs of higher animals. The mouth (o) is an 

 oval slit, and is fringed with gristly filaments. The 

 lancelet has no brain, heart, bones, skull, ears, or 

 kidneys. It is the only vertebrate which wants a 

 heart, and it is likewise the only vertebrate in which 

 the blood is colourless. Along the back runs the 

 only representative of the skeleton namely, a soft 

 rod-like body, called the notochord (n). This struc- 



Fig. 10. The Laucelet (Amphioxus lanceolatus\ enlarged to twice 

 its natural size, (o Mouth ; 6 Enlarged pharynx ; g Stomach ; 

 h Sac representing the liver ; i Intestine ; a Anus ; n Noto- 

 chord ; / Rudiments of fin-rays ; p Abdominal pore.) 



ture, by the way, is found in the early development 

 of every vertebrate animal, being replaced in all, 

 save a few fishes, as time passes, by the spine itself. 

 Above this rod lies the nervous cord of the lancelet. 

 The mouth opens into a very wide throat or pharynx 

 (b) } whose walls are perforated with slits that open 

 into the cavity of the body. The walls of this great 

 throat are richly set with the microscopic processes 

 called cilia, which, by their incessant waving, cir- 



