512 
(I. H. GBOSVENOR AND GEOFFREY SMFrH. 
made from dry horse-dung. The actual numbers obtained by 
him in these early experiments were as follows : 
Mo in a re c t i r o s t r i s : Oxford, 1904. June, July and October. 
j Isolated. 
1 . 
Crowded. 
i 
j No. of <J s. 
No. of $ s. 
Xo. of c5 s. 
Xo. of 9 s. 
i 
j 4 
95 
50 
153 
4'296 per cent, males. 
24 6 per cent, males. 
M o i n a m a c r o c o p a : Oxford, 1904. J uue and J uly. 
Isolated. 
Crowded. 
Xo. of (J s. 
Xo. of 9 s. 
1 
No. of ds. No. of $8. 
25 
224 
L 
1 
10% per cent, males. 
30'89o per cent, males. 
From these figures it will be seen that when the partheno- 
genetic females were kept isolated they produced 4'2 per cent, 
and 10 per cent, males, but that when they were kept crowded 
together but otherwise under identical conditions they 
produced 24’6 per cent, and 30’8 per cent, males. 
In 1906 Grosvenor asked me to join him in repeating and 
extending this investigation, and during the summer and 
autumn of that year we bred Moina rectirostris on a large 
scale and subjected them not only to the conditions of isolation 
and crowding, but also to different temperatures. Weobtaiued 
the Moina from a small pond at Sutton near Stalham on the 
Norfolk Broads, and most of the experiments were done in the 
fresh-water laboratory belonging to Sir Eustace .and Mr. 
Robert Grurney, to whom we offer our thanks for giving us 
every accommodation in their laboratory. 
