THE WORMS 71 
within sandy beaches in tubular burrows lined with mucous, and 
the situation of the burrow is always marked by a heap of coiled 
string-like masses of sand cast out at its mouth. The creature is 
about five inches long and so delicate that its own weight is suffi- 
cient to break it into pieces, so that it must be dug and washed out 
of the sand with great care. The front end of the body is, how- 
ever, quite tough and muscular, and is elongate and .acorn-like in 
shape; although it is often expanded and contracted in life. Back 
of this acorn there is a thickened, collar-like region, and then comes 
the long, tapering, worm-shaped body. The acorn is usually yeliow 
or dull orange, the collar darker orange, and the body greenish- 
brown or brownish-purple, often mottled with dull white spots. 
The mouth is at the lower front edge of the collar, and the creature 
feeds upon the minute organisms contained in the large quantities 
of sand which it swallows. The intestine extends straight through 
the body. The sides of the intestine in the forward part of the 
body are pierced, however, by numerous gill clefts which open to 
the outside ina series of pores along both sides of the middle of the 
back. Now, gill slits are peculiar to the vertebrates, being found 
either in embryonic or adult life in every known vertebrate from 
the lowest fishes up to man. Indeed, many naturalists have sup- 
posed that Balanoglossus might be a survivor of the ancient race 
which long ago gave rise to the vertebrates. On the other hand the 
larva of Balanoglossus is free-swimming, and bears such a remarkable 
resemblance to that of a starfish, or Echinoderm, that no one sus- 
pected it to be anything else until it was reared and observed to 
change into a Balanoglossus. It is possible, therefore, that Balano- 
glossus is descended remotely from ancient forms which gave rise 
to both the annelid worms and the Echinoderms. The discussion 
of this interesting subject would, however, take us too far afield, 
and the reader is referred to the table of references for further 
accounts of this species. 
