302 EVENINGS AT THE MICROSCOPE. 



are tlirust out and withdrawn in constant succession, as 

 :lie body is ever lengtliening and sliortening. 



Let us exchange this little freshwater Worm for a 

 marine one. Here is a JPolynUe^ a curious genus, very 

 common under stones at low water on our rocky shores. 

 It is remarkable on several accounts. All down the 

 back we discover a set of oval or kidney-shaped 

 plates, which are called the back-shields {dorsal elytra) \ 

 these are flat, and are planted upon the back by little 

 footstalks, set on near the margin of the under surface : 

 they are arranged in two rows, overlapping each other 

 at the edge. These kidney-shaped shields, which can be 

 detached with slight violence, are studded over with 

 little transparent oval bodies, set on short footstalks, 

 which are perhaps delicate organs of touch. The inter- 

 mediate antennse, the tentacles, and the c^Vr^', or fila- 

 ments of the feet, are similarly fringed with these little 

 appendages, which resemble the glands of certain 

 plants, and have a most singular apjDcarance. If we 

 remove the shields, we discover, on each side of the 

 body, a row of wart-like feet, from each of which pro- 

 ject two bundles of spines of exquisite structure. The 

 bundles, expanding on all sides, resemble so many 

 sheaves of wheat, or you may more appropriately fancy 

 you behold the armoury of some belligerent sea-fairy, 

 with stacks of arms enough to accoutre a numerous 

 host. But if you look closely at the weapons them- 

 selves, they rather resemble those which we are accus- 

 tomed to wonder at in missionary museums — the arms 

 of some ingenious but barbarous people from the South 

 Sea Islands — than such as are used in civilised warfare. 

 Here are long lances, made like scythe-blades, set on a 

 staff with a hook at the tip, as if to capture the fleeing 



