18 MORGAN. [Vou. IX. 
path of the anterior-ciliated band cannot be any longer seen 
in surface views. At the base of the proboscis, and a little to 
the left of the median-dorsal line, will be seen the external 
opening of the anterior body-cavity. The irregular outline of 
the proboscis vesicle is seen through the body-wall in this 
region. 
Immediately behind the collar groove and quite widely sepa- 
rated from one another are two pits or invaginations of the 
ectoderm. These are the foundations of the collar pores and 
gill openings. At this stage they are mere pits in the ectoderm. 
Dividing the body into two nearly equal parts is the circular 
ciliated band. Its cilia are much shorter than in the preced- 
ing stage, and the band itself where the cilia are attached 
is narrower. The band is marked by black-brown pigment. 
Scattered pigment flecks are also found over the ectoderm of 
the body. 
The outline of the digestive tract is seen through the body- 
wall. It is still roughly divisible into three regions. The 
oesophagus shows three pairs of protrusions which are the gill- 
pouches. These are not fused as yet at any point with the 
ectoderm. The stomach is oval and its walls are, as seen in 
the living larva, quite thick. It is separated by a constriction 
from the intestine, whose walls are also proportionately thicker 
than before. At times, when the ventral side of the animal 
was turned toward the observer, the large mouth could be seen. 
It lies just within the collar, at the base of the proboscis. 
After its entrance into the sand the larva increases at first 
rapidly in length, so that at the end of twelve hours it has 
reached the size shown in Fig. 7, Pl. I (dorsal view). I find 
in my notes that the larva here figured was caught in the 
net June 24, at 12 mid-day, and that it was drawn June 25 
at three o'clock p.m. Further, that over night (or approxi- 
mately for twelve hours) it had been buried in the sand. The 
color of the young worm when alive is milky white and the 
whole animal is still semi-transparent. A pair of brown-black 
eyes are still to be found at the anterior end of the proboscis, 
and the whole body is flecked with brownish pigment. The 
