DAPHNIADiE. 
79 
wheel completely round the pond. Should the mass come 
near enough the edge to allow the shadow of the observer 
to fall upon them, or should a dark cloud suddenly 
obscure the sun, the whole body immediately disappear, 
rising to the surface again when they have reached beyond 
the shadow, or as soon as the cloud has passed over. 
They are very prolific, giving birth to their young a great 
many times during their lives, and some of the larger 
species having as many as forty or fifty eggs and upwards 
in their matrix at once. According to Jurine, in June 
the young ones begin to have eggs, about ten days after 
their birth, and it is probable they continue to produce 
all the summer through at frequent intervals. The males 
are very few in number, compared with the females, and 
are only to be met with at certain seasons, generally, as far 
as my observation goes, in autumn. From this circum- 
stance, Schceffer and others have considered them as her- 
maphrodites; and Sulzer (as quoted by Straus), though 
he oppugns this opinion, gives a more singular one still, 
believing that a copulation might take place with the 
young before they see the light of day ! These authors 
had never seen the males, nor ever witnessed the act of 
copulation. Muller and others, however, detected the 
male, and witnessed the act ; and it is now clearly ascer- 
tained that one single copulation is sufficient not only to 
fecundate the mother for her life, but all her female de- 
scendants for several successive generations. This was 
observed by Schoeffer, who followed them up to the fourth, 
by Straus to the fifth, and by Jurine to the sixth ; the latter 
observing that he thinks it probable it might extend in 
some species to the fifteenth generation. Extraordinary 
as this may appear, I have further found that the young 
produced from the ephippial eggs are also fecundated by 
this one copulation, and have progeny; and that their 
young again also produce eggs without the intervention of 
the male. I have followed up the successive generations, 
as far as the fourth, in the Daphnise born in the usual 
manner, and as far as the third, in those born from ephip- 
