HEDGE AND DITCH 171 



the surface when the light is weak, but sink when the sun 

 shines upon the pool. 



The water-flea, being very abundant and easily kept in 

 captivity, is an excellent study for the young naturalist, 

 who, let us suppose, has just come into possession of a 

 microscope. I would recommend such an one, if he really 

 means to improve, to put aside all the favourite curiosities, 

 and not to distract his mind by frequent change of object. 

 Let him observe steadily and patiently some one living 

 thing, until he has mastered his instrument and learned 

 how to work. A fair set of drawings of Daphnia, made 

 without the help of books, would give proof of the kind 

 of ability which really advances natural history. Few will 

 take the advice, and we must leave the majority to their 

 cabinets of bought slides. 



When the general structure of the water-flea has been 

 made out, I would suggest that its modes of egg-produc- 

 tion should be particularly studied, as it is chiefly these 

 which have made Daphnia notable to every biologist. 



Remark first that all the water-fleas that we have fished 

 out of the pool are of one sex. Such as are full-sized bear 

 eggs in some stage of development. When mature, the 

 eggs are lodged, two or three together, in a recess (the 

 brood-pouch), which lies between the carapace and the 

 back of the body ; now and then a fresh-hatched water- 

 flea may be seen imprisoned in this space, waiting till the 

 mother moves aside some long spines which close the 

 passage, and so allows it to escape. Before the eggs were 

 passed into the brood-pouch, they lay in the ovaries, long 

 paired organs, situated below and to either side of the 

 alimentary canal. The duct by which the eggs escape 

 into the brood-pouch can rarely be seen except when a 

 dark egg is passing along it. Since there are no males at 

 this time of year, all these eggs are unfertilised, but they 

 develop none the less, and the new generations succeed 

 one another with great rapidity. 



At the approach of winter our common water-flea pro- 



