46 MR. R. GURNEY ON THE LIFE HISTORY OF THE CLADOCERA. 
bodies were not true eggs, but internal “ buds ” or “ pseudova” 
comparable to the buds of Coelenterata. Von Siebold (1856)* 
was the first to prove that the reproduction of the Cladocera 
and certain other Crustacea was parthenogenetic, or by 
means of true eggs not requiring fertilisation, but even then 
his conclusions were disputed — for instance, by Leydig 
(i860). | 
At certain times of the year, particularly in autumn, males 
appear also and sexualj reproduction occurs, generally 
together with parthenogenetic, but sometimes replacing it 
entirely. The fertilised eggs are quite different from the 
agamic eggs. Their yolk, instead of being in large, clear 
globules, is in the form of small dark coloured granules, 
giving the egg a very dark appearance and hiding the nucleus. 
They are also radically different in their origin, requiring the 
absorption of many more “ nurse cells ” than the summer 
eggs do. They are also protected by a rather thick shell. 
These fertilised, or “ resting,” eggs are laid in the usual way, 
but they do not develop at once, being destined to be shed 
with the moulted shell and, when laid in autumn, to rest 
during the winter and to hatch in the following spring. 
They will bear complete drying and freezing, and are actually 
the better for it. They may be kept for years in the dry 
state. In fact, much of our knowledge of exotic Cladocera 
has been acquired by hatching them from eggs contained in 
mud sent to Europe for the purpose. It is by their means 
that the species are preserved from extinction by frost and 
the drying up of water. It is only a few species that shed 
their eggs free in the water, and in these species, e.g., Sid a 
crystallina, probably the unprotected eggs would not bear 
so much as those of other species. In the majority of cases 
the eggs are protected by a specially modified part of the 
shell known as the Ephippium. In the Daphnidae, where 
* ‘ Wah re Parthenogenesis bei Schmetterlingen und Bienen.’ Leipzig, 1856, 
P- 138. 
t ‘ Naturgeschichte der Daphniden.’ Tubingen, i860. 
X I use the word “sexual” in opposition to “ parthenogenetic” simply for 
convenience. Of course parthenogenetic reproduction is really sexual. 
“ Amphigonic” and “Agamic” reproduction would be more correct. 
