BALANOGLOSSUS, A CONNECTING LINK 



(After Spengel) 



Widely distributed in the sand of many seas are the 

 Enteropneusts (i.e., gut-breakers), which help to link 

 backboneless (Invertebrate) and backboned (Verte- 

 brate) animals. Are they Vertebrate-like worms or 

 worm-like Vertebrates? They are connecting links, 

 though it does not follow that they are directly an- 

 cestral to the Vertebrates we know. The proboscis 

 (PR) is used for burrowing in the fine sand; M shows 

 the position of the mouth; C is the region called the 

 collar; GS are numerous gill-slits opening from the 

 food-canal to the exterior, a Vertebrate feature never 

 seen in Invertebrates ; CG, a slight ciliated groove 

 along the dorsal middle line; GL, glandular saccula- 

 tions on the food-canal, shining through the skin. The 

 animal figured is about six inches long. In several 

 ways there are distinct hints of Vertebrate affinities. 



79 



