DEVELOPMENT OF CUCUMARIA ECHINATA 937 
a similar feature occurs in Stichopus japonicus also, 
judging from the figure given by Mitsukuri (80, 1908, p. 12, 
fig. 3). Here the posteriormost unpaired one seems to be the 
first to appear, and besides it the mid-ventral canal seems to be 
provided with three pedicels to the left and one to the night, 
whereas each of the ventral radii has three pedicels. 
16. SUMMARY. 
1. The breeding season of Cucumaria echinata seems 
to begin in the middle of June and to last until the early part 
of August. During that season the wall of the genital tubes 
is thin, but in an inactive period it is very thick. No muscle 
layer could be made out in the wall. The genital papilla is 
subdivided, the branches being more numerous in males than in 
females. Both sexes occur in almost equal numbers. 
2. The ovarian egg is attached to the wall of the genital tube 
by its broad vegetative half. At the animal pole which is 
directed towards the internal lumen of the tube a short rod-like 
cytoplasmic process is found. This structure develops near the 
end of the growth of the egg, and probably has some significance 
in relation to future changes of the egg. 
3. Freshly captured mature animals spawn in the evening. 
At first the males shed out spermatic fluid, and after some minutes 
the females begin to lay eggs. During these acts no special 
movements of tentacles are observed in either sexes. 
4. The newly-shed egg is slightly flattened and measures about 
390-400 » in diameter. It is covered with a gelatinous layer, 
through which a canal opens at the animal pole. The egg is 
heavier than sea-water. 
5. The first polar body has been formed by the time it is shed, 
when the second maturation spindle is to be seen. The spermato- 
zoon enters the egg before the second maturation division, and 
probably at the point near to, but not precisely identical with, 
the animal pole. 
6. The first cleavage spindle is formed within an hour. The 
cleavage is total and equal, proceeding quite regularly up to 
about the thirty-two-cell stage. Very often an interlocking 
