204 
NOTES AND MEMORANDA. 
to that in which, among the generations sprung from that Naiad, there 
are found again sexual distinctions, has not been studied in all its 
phases, and it is still a question whether the same individuals (zooides) 
are gemmiparous and sexual, or if the sexual and agamous reproduc- 
tions are strictly distributed over different individuals or generations. 
As for the other two groups of Anellides in which agamous repro- 
duction has been observed hitherto, namely, the Syllides and the 
Sepulides, the question is almost at the same point. For these reasons, 
the Society desires to urge a thorough research, and one answering 
the actual demands of science, of agamous reproduction and all the 
points pertaining to it, of one of the groups of these setiferous Anel- 
lides. It therefore offers its gold medal as a prize to the one who 
shall solve this question in a satisfactory manner, either for one or 
several species of the group of Naiades (comprising Cinetogaster) or 
for one or several species of Syllides or Tubicolides. The papers 
should be accompanied by the necessary drawings explaining the 
points on which the researches have especially borne. The answers 
to these questions may be written in Latin, French, English, German, 
Swedish, or Danish. The papers must not bear the name of the 
author but a motto, and must be accompanied by a sealed note, 
furnished with the same motto, enclosing the name, profession, and 
address of the author. The members of the Society who live in 
Denmark do not take part in the competition. The prize awarded for 
a satisfactory answer to the question proposed is the gold medal of the 
Society (value, about 20Z.). Papers must be addressed before the end 
of October, 1873, to the Secretary of the Society, Counsellor J. Japetus 
Sm. Steenstrup, Copenhagen. 
Photographing Amphipleura pellucida. — Dr. J. J. Woodward 
gives, in a late number of the ‘ American Naturalist,’ an able paper, 
accompanied by a photographic plate of great excellence, on the sub- 
ject of photographing A. pellucida. After describing other means 
of conducting the operation, he states that that by sunlight involves 
least trouble and expense, and may be best managed as follows : — 
Erect a perpendicular wooden screen about two feet square on one 
edge of a small table. Cut in this a circular hole an inch and a half 
in diameter at about the height of the under surface of the stage of the 
microscope. On the outside of this hole mount a small plane mirror 
which can be adjusted by passing the hand to the outside of the screen. 
On the inside, cover the hole with the ammonio-sulphate cell. (A 
piece of dark blue glass will answer the purpose, though not so well). 
Now move the table to a window through which the direct rays of the 
sun can fall upon the mirror; adjust this so as to throw a nearly 
horizontal pencil of parallel rays through the hole, and place the 
microscope in the shade of the screen in such a position that the 
parallel blue rays will fall on the under surface of the Amphipleura 
slide at an angle of from 50° to 75° with the plane of the slide (I 
suppose the frustule to be examined has first been found by ordinary 
daylight or lamplight). Next place a small bull’s-eye or any other 
condenser of from one to three inches focal length (mounted on a 
separate stand or on a radial arm) in the parallel pencil in such a 
