STUDIES IN ANIMAL LIFE. 51 



but there are curious indications of positive retro- 

 gression from a higher standard in the metamor- 

 phoses of some animals. Thus the beautiful marine 

 worm Terebella, which secretes a tube for itself, and 

 lives in it, fixed to the rock or oyster-shell, has in 

 early life a distinct head, eyes, and feelers ; but in 

 growing to maturity it loses all trace of head, eyes, 

 and even of feelers, unless the beautiful tuft of 

 streaming threads which it waves in the water be 

 considered as replacing the feelers. There_are the 

 Barnacles, too, which in the first stage of their ex- 

 istence have three pairs of legs, a very simple single 

 eye, and a mouth furnished with a proboscis. In 

 the second stage they have six pairs of legs, two 

 compound eyes complex in structure, two feelers, 

 but no mmith. In the third, or final stage, their 

 legs are transformed into prehensile organs, they 

 have recovered a mouth, but have lost their feelers, 

 and their two complex eyes are degraded to a single 

 and very simple eye-spot. 



But, to break up these digressions, let us try a 

 sweep with our net. We skim it along the surface, 

 and draw up a quantity of duckweed, dead leaves, 

 bits of stick, and masses of green thread of great 

 fineness, called Conferva by botanists. The water 

 runs away, and we turn over the mass. Here is a 

 fine water-beetle, called the "Water-tiger," from its 

 ferocity (Fig. 12). You would hardly suspect that 

 the slim, big-headed, long-tailed Water-tiger would 

 grow into the squat, small-headed, tailless beetle ; 



