THE NOTOCHORD AND ALIMENTARY CANAL 445 
the formation of the vertebrate alimentary canal was a repetition of 
the same process which had already led to the formation of the 
notochordal tube. The formation of the anterior part of the ali- 
mentary canal in Ammoccetes at the time of transformation strongly 
suggests the marked similarity of the two processes. 
Of all the startling surprises which occur at transformation, this 
formation of a new anterior gut is the most startling. From the 
oral chamber of Petromyzon two tubes start: the one leads into the 
gill-chambers, is known as the bronchus, and is entirely concerned 
with respiration ; the other leads without a break from the mouth 
to the anus, has no connection with respiration, and is the alimentary 
canal of the animal. Any one looking at Petromyzon would say 
that its alimentary canal was absolutely non-respiratory in character. 
Before transformation, this kind of alimentary canal commences at 
the end of the respiratory chamber ; from here to the anus it is of 
the same character as in Petromyzon, but in Ammoccetes the non- 
respiratory anterior part simply does not exist: the whole anterior 
chamber is both respiratory and affords passage to food. This part 
of the alimentary canal of the adult is formed anew. We see, then, 
here the formation of a part of the alimentary canal taking place, not 
in an embryo full of yolk, but in a free-living, independent, grown-up 
larval form in which all yolk has long since disappeared: a condition 
absolutely unique in the vertebrate kingdom, but one which more 
than any other may be expected to give a clue to the method of 
formation of a vertebrate gut. 
The formation of this new gut can be easily followed at trans- 
formation, and was originally described by Schneider. His statement 
has been confirmed by Nestler, and its absolute truth has been 
demonstrated to me again and again by Miss Alcock, in her specimens 
illustrative of the transformation process. First, in the mid-dorsal 
line of the respiratory chamber a distinct groove is formed, the 
edges of which come together and form a solid rod. This solid rod 
blocks the opening of the respiratory chamber into the mid-gut, so 
that during this period of the transformation no food can pass out of 
the pharyngeal chamber. A lumen then begins to appear in this 
solid rod at the posterior end, which steadily advances mouthwards 
until it opens into the oral chamber and thus forms an open tube 
connecting the mouth with the gut. 
Here, then, is the foundation of a new gut on very similar lines 
