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The pLankion
investigations.
This result is obviously definitely opposed to the view quoted above as being put forward
by C. Apstein, 1911, that Ph. (Ph.) globosa has a single planktonic copulation period limited
to the months of April, May and June.
On account of this I carried out new investigations concerning this problem. In the first
place I investigated about a hundred plankton samples, taken during January, February, May
and July at Skager Rak and Cattegat by the investigation vessel „S k a g e r a k“ for the
,,Swedish Hydrographical Biological Commission“. Secondly the plankton tables published
by the „Conseil permanent international pour l’exploration de la mer“, on whicli C. APSTEIN
had founded his view, were subjected to a renewed and careful investigation.
The results of the ürst investigation seemed to support the view put forward by APSTEIN.
In all the samples from January, February and July this species was quite absent. Only in
a few samples from the month of May, consequently within the period suggested by APSTEIN,
did I succeed in finding it. Both males and females were discovered. This is interesting because
the literature so far published does not clearly show whether both sexes are found swimming
freely in the higher layers of the water. The results are shown in the following table:
Surface 20 m. 25 m. A few metres from the bottom
Outside Varberg 8. V. 1912, 11—12 p. m. 21 d, 1 $ 0 3 J Y $ 33 d, 2 $
Outside Varberg 9. y. 1912, 1—2,30 a. m. 68 o, 1 ? 10 d 0 65 d, 1
At Anholt 28. V. 1912, 1,30—1,50 a. m. 0 0 0 2d
The small number of females seems to indicate that the females return to the bottom
more rapidly than the males.
The following are the results of my re-examination of the plankton tables published by
the „Conseil permanent“:
Phüomedes (Ph.) globosa is stated in these tables to have been caught at the following
stations on the following occasions: (The same terms are used in my work as those in these tables:
cc means very common, c common, + „neither common nor rare“, r rare, rr very rare, — means
that the species was not found).
1903: May: Da 7, lat. 57° 52’ N., long. 11° 18’ E., depth to the bottom = 87 m.
2. V., 1 h io a. m. — 2 11 20 a. m.
75 m. — 45 m. rr.
65 ,, — 0 ,, +
10 „ — 0 „ rr.
6 » +•
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