66 The Bird 
hints of the way it originated. In the lowest of fish-like 
creatures—the Amphioxus, a tiny animal, an inch or two 
in length, living in the sand along our shores—there is 
a thread-like cord of a gelatinous substance (not carti- 
lage, however) extending down the back, known as the 
notochord. He looks like some kind of worm, but this 
little gristle is his badge of nobility and lifts him clear 
Fig. 42.—Amphioxus, one of the lowest vertebrates, with a mere thread of 
gristle foreshadowing the back-bone of higher animals. This creature bur- 
rows in the sand along the Atlantic coast. 
of corals, snails, insects, and worms, into the realm of 
back-boned animals. This notochord lies underneath a 
thin white line which is all the spinal chord he has, and, 
at the front end of this, a tiny dot of pigment stands 
for brain, eye, and ear. Indeed Amphioxus has neither 
skull, brain, nor limbs. 
The history of the back-bone, like human history, is 
not altogether a majestic upward evolution; it has its 
tragedies and set-backs, its hopes and failures. In the 
waters along our Northern seashores are creatures, some 
sponge- or lichen-like, others with strange bulb-like bodies 
