142 
them away from the aquarium too soon, since it turned out that 
only comparatively few of them had been fertilized. Moreover a 
large percentage of those developed abnormally. But fortunately 
some few of them developed normally. After three days they be¬ 
gan to assume the shape of small Plutei with the first rudiments 
of the skeleton. At the age of 7 days the postoral and postero- 
lateral rods had begun to form, and on the lower part of the latter 
the small recurrent rod so characteristic of Ophiopliiteus manens 
had appeared. The postoral arms had a prominent red pigment 
spot in the point. — Although 1 did not succeed in rearing the 
larvæ beyond this point, it was hereby definitely ascertained that 
Ophiopluteus maneus is the larva of Amphiura fili- 
f o r m i s. 
Wishing, of course, to try to rear the larva of Amphiura Chi- 
ajei also, I continued the experiment with this species. A doser 
examination showed that it was not yet ripe at the time, when 
Amphiura filif'ormis was at the height of its breeding season, in 
the first part of August. It was only in the beginning of September 
that its breeding season began. About this time a number of the 
most ripe specimens to be found were put into an aquarium pre- 
pared in the same way as before. On the 9th of September I had 
then the great pleasure of seeing a pair of males rise above the 
mud in the same way as Amphiura filiformis. I was, however, 
surprised in seeing that the sperm did not spread as a milky cloud 
in the water; it sank to the bottom in thick masses. On examin- 
ing the sperm under the microscope I found that the spermatozoa did 
not move at all. The reason for this was evident enough. At the 
time when Amphiura filiformis was breeding the salinity of the 
water used for the aquaria was about 32 %o; now the salinity 
was only about 28 °/oo. The immobility of the sperm (which I tried 
in vain to raise by making the water more alkaline) was evid¬ 
ently due to the salinity being too low, and this easily accounts 
for the faet that no females rose to discharge their eggs, the chemo- 
tactic action of the living sperm, which must be supposed other- 
wise to induce the females to sexual activity, being eliminated in 
this case. 
It is very noteworthy that, in spite of the lover salinity, the 
Amphiuras themselves lived quite well in the aquaria, taking the 
