178 EVENINGS AT THE MICROSCOPE. 



ing water finds its way in currents, bringing oxygen to be 

 respired and food to be devoured. 



The translucent shell descends in front into a sharp 

 long beak, below which are seen the organs of the mouth, 

 two pairs of foot-jaws, beset with fine bristles. At the 

 origin of the beak is the eye, consisting, as we saw in the 

 Cyclops, of several lenses, enveloped in a common cornea, 

 the whole forming a movable organ of a blue-black hue. 

 Just behind this, at the very highest part of the shell, 

 is a little colourless bladder-like vesicle, which constantly 

 maintains a rapidly alternate contraction and dilatation. 

 This is the heart, and this motion circulates the blood. 



Below this, there is seen a great translucent irregular 

 mass of flesh, evidently comprising many viscera, which 

 winds along from one end of the shell to the other, nearly 

 occupying its entire area. It is not in connexion with it at 

 the hinder part, as we see by its free movements there, 

 where it curves round, and, bending beneath, terminates in 

 a blunt tail, armed with two strong hooks, which can at 

 pleasure be thrust down through the narrow orifice of the 

 shell and become partially straightened by being forcibly 

 thrown backward. This great central mass is mainly 

 occupied by the alimentary canal, in which food in various 

 stages of assimilation may at all times be seen, and in 

 which the interesting function of digestion can be wit- 

 nessed throughout, from the first seizure of the atom and 

 its mastication by the jaws, to the discharge of the useless 

 remains. 



The individual before us does not carry at this time 

 eggs in the process of development ; but the deficiency is 

 supplied by a Daphnia which is playing about in the same 

 drop of water. Here you perceive, between the arched 

 outline of the shell and the sinuous outline of the free 

 soft body, an open space of some size, which constitutes a 

 receptacle, in which the eggs are deposited as they are 

 laid, and in which they remain not only until the little 



