20 MORGAN. [Vou. IX. 
the gill-slits, and later, as we shall see, come into a secondary 
connection with the first pair of gill-slits. 
I regard this as an important point and have given a good 
deal of attention to it, but we shall study it at greater length 
in the second part of the paper. 
Spengel, in 1877, described the collar pores as arising from 
the first pair of gill-slits. I believe, however, that the connec- 
tion is entirely a secondary one. In 1891 I saw in one larva of 
the New England Tornaria the formation of the first pair of 
gill-slits, and found that the ectodermal invaginations communi- 
cated with the second pair of pouches of the digestive tract. 
I left the question open as to whether or not this was an 
abnormal condition inasmuch as my results were obtained from 
a single larva kept for 70 hours in an aquarium. I am inclined 
to believe now that in this respect the development was 
abnormal, and that the first pair of gill pouches should have 
opened to the exterior before the second pair did so. 
In stages of the Bahama larva, between those of Fig. 6 and 
Fig. 7, we find that the first pair of gill-pouches opens to the 
exterior some time before the second pair opens. 
The outlines of the digestive tract can be seen through the 
body wall. The alimentary canal is a simple tube running the 
whole length of the body. The figure does not show its 
division into three parts, although the distinction is to some 
extent still to be found. The constriction between the stomach 
and intestine has almost disappeared, and it will be seen that 
the intestine has elongated to a very slight extent as compared 
with the elongation of the stomach. The ‘stomach,’ in fact, 
forms the greater length of the tube, and itself suggests 
the term intestine more than does the small posterior division 
called by that name, indicating, as before noticed, the conven- 
tionality of the terms already applied to the earlier stages. 
The young worm continues to enlarge and grow in length. 
In Fig. 8, Pl. II, is shown a later stage (dorsal view). The 
larva was caught on June 23 and killed on June 27 (the exact 
times of day not recorded). The young worm had been in 
captivity for four days (or about ninety-six hours). At this 
