'^'•'•y' I Searle, The Pond and its Inhabitants. o 



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head. In shape it resembles a blackberry, having a number 

 of lenses surrounding a mass of black pigment. It is well 

 supplied with muscles, and is connected by an optic nerve 

 with the ganglia, or brain. 



Not the least remarkable feature in the life-history of Daphnia 

 is the mode of reproduction. In the ovary of the female 

 parthenogenetic eggs are formed — that is, eggs that have the 

 power of segmentating and developing into a new animal 

 without having first been impregnated and fertilized by 

 spermatozoa from a male. These eggs develop into female 

 Daphnias, and they in turn produce parthenogenetic young ; 

 and the process may go on for quite a number of generations 

 without ever a male being seen. Then through some unknown 

 caiise — it may be through food becoming scarce — some males 

 are hatched, and copulation between the sexes takes place. 

 The eggs resulting from this union differ in a remarkable way 

 from the parthenogenetic eggs. These latter were numerous, 

 perhaps twenty or thirty being laid at a time, and these were 

 carried about in the brood chamber of the carapace of the 

 mother until the young were hatched. On the other hand, 

 the fertilized eggs — two only in number— are enclosed in the 

 ephippium, or saddle, of the carapace, which gradually thickens 

 around them, and remain there until the next moult, when 

 the ephippium with its embedded eggs are cast off. These 

 ephippial or resting eggs, as they are called, are enclosed in a 

 horny shell, and possess remarkable vitality. They may be 

 dried up for years, and be blown about by the wind during 

 long periods of drought ; and yet, when the wet season 

 returns, and the pools again fill with water, these eggs hatch 

 out as female Daphnia, and the life-cycle is again carried 

 through. 



As a recorded instance of the vitality of these eggs, it may 

 be mentioned that some years ago a number of Daphnia eggs 

 wi^re gathered up with the dry sand on the shore of Lake 

 Burrumbeet, and stored in a glass bottle fitted with a screw 

 metal top. Every year a portion of this material was placed 

 in a vessel filled with clean water, when a number of the eggs 

 would hatch out. These hatching operations were repeated 

 with success for five years. The following year the remaining 

 portion of the material was divided into two parts. One of 

 these was sent to a scientist in Norway, while the other was 

 placed in a vessel of water, as on previous occasions. From 

 both of these samples young Daphnia were hatched. The 

 experiment proved that the eggs of Daphnia could remain 

 dried for a period of at least six years, withstand a voyage 

 through the tropics, and still retain their vitality, so that when 

 placed in water they hatched out as young Daphnia at the 



