8 MORGAN. [VoL. IX. 
the middle of the side it makes a sudden small upward bend, 
falling again before taking its upward course. Its upward or 
anterior course runs a little to one side of the middle line. In 
this part of its course it is drawn out into about eight tentacle- 
like projections above the surface. The band turns back 
(posteriorly again) to run a course almost parallel to its last. 
Here it is again drawn out into eight or nine tentacles. Before 
reaching the mid-dorsal surface it turns forward again, and is 
again drawn out into eight or nine tentacles. . 
Just beneath the apex of the larva the band turns suddenly 
forward to disappear in the apical plate. The structure of the 
apical plate is dealt with below. On the ventral lateral side of 
the plate a similar (or the saze) band emerges to run down- 
ward (ventro-laterally) with its eight or nine tentacles, then 
turns again forward with more tentacles and again posteriorly 
with the eight tentacles to turn finally towards the ventral 
surface passing in front of the mouth-opening to repeat its 
course on the opposite side. 
It is often desirable for purposes of description to map out 
the surface of the larva, and I suggest the following terms : 
The whole of the area included wzthzz the anterior band — the 
area containing the large black dots of the figure —may be 
called the circum-oral area. It is divided into four sub- 
regions: the ventral-lateral area, the dorsal-lateral area, the 
middle-lateral area, and the posterior-ventral area. 
The area lying outside of the anterior band and between it 
and the posterior band (assuming it continuous across the 
apical plate) is the extra-oral. The area of the posterior plate 
(not seen in side view), lying within the posterior circular band, 
may be spoken of as the posterior plate. 
Large jet-black pigment dots are found in the circum-oral 
area, as seen in the figure. They are seen to project in the 
living animal from the surface and produce the effect of large 
parasitic bodies clinging to the outer surface. Sections show, 
however, that they are constituent parts of the ectoderm as 
will be described later. 
If we examine in detail the apex of the larva we find the 
ectoderm thickened, forming an apical plate containing two 
