Videnskabelige meddelelser

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Videnskabelige meddelelser

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them away from the aquarium too soon, since it turned out that

only comparatively few of them had been fertihzed. 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 Ophiopluteiis manens

had appeared. The postoral arms had a prominent red pigment

spot in the point. ^ Although I did not succeed in rearing the

larvæ beyond this point, it was hereby definitely ascertained that

Ophiopluteus mancus is the larva of Amphiura filiform

i s.

Wishing, of course, to try to rear the larva of Amphiura Chi-

(tjei also, I continued the experiment with this species. A closer

examination showed that it was not yet ripe at the time, when

Amphiura /iliformis 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 Ampliiura filiformis was breeding the salinity of the

water used for the aquaria was about 32 ^ oo ; now

the salinity

was only about 28 %o. 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

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