PLANARIA ARETHUSA. 105 



proved to have come from a species of the 

 entomostraca, a small shelled animal, which, 

 according to my calculation, should not 

 have laid an egg one-third as large, and 

 whose presence in the water had been over- 

 looked. Thus if these planariae propagate 

 by eggs, they are still undiscovered. 



Yet here also the wisdom of Nature has 

 not failed in providing for the preservation 

 of the race ; — spontaneous division ensues, 

 whereby, as before, a fragment detaching 

 itself from the body of the parent, becomes 

 a perfect animal, while the mutilated por- 

 tion of the trunk is repaired. 



The diversity of colour in the same pla- 

 nariae first excited my conjectures, that re- 

 production after spontaneous separation had 

 taken place. Six animals were therefore 

 selected for farther observation, four of 

 large, and two of small size. The second 

 day subsequent, which was the fifth of No- 

 vember 1810, I remarked that one of the 

 larger had lost a fragment from the tail, not 

 exceeding a sixth part of the length of the 



