200 THE MICROSCOPE. 



bears a sharp calcareous piece called the sagitta, or arrow. This can be 

 pushed out at the pleasure of the animal, serving to roughen the sur- 

 face of the tentacle, and afford a much firmer hold of its living prey. 



The polyp increases rapidly : a portion of the body swells, a young 

 one puts forth its head from the part, its arms begin to grow, it then is 

 industrious in catching food, its body communicating with that of its 

 parent, and participating • in the fears and actions of its progenitor ; 

 finally, it is cast off to wander the world of waters. Betimes, ere yet 

 free from parental attachment, it has two generations on its own body. 

 Four or five offspring are thus produced weekly. But the most ex- 

 traordinary circumstance in respect to this creature is thus described 

 by M. Trembley : " If one of them be cut in two, the fore part, which 

 contains the head and mouth and arms, lengthens itself, creeps, and 

 eats on the same day. The tail part forms a head and mouth at the 

 wounded end, and shoots forth arms more or less speedily, as the heat 

 is favourable. If the polyp be cut the long way through the head, 

 stomach, and body, each part is half a pipe, with half a head, half a 

 mouth, and some of the arms at one of its ends. The edges of these 

 half pipes gradually round themselves and unite, beginning at the tail 

 end ; and the half mouth and half stomach of each becomes complete. 

 A polyp has been cut lengthways at seven in the morning, and in 

 eight hours afterwards each part has devoured a worm as long as 

 itself." 



Still equally wonderful is the fact, that if turned inside out, the parts 

 at once accommodate themselves to their new condition, and carry on 

 all their functions as before the accident. Indeed, this animal seems 

 so peculiarly endowed with the germs of vitality in every part of its 

 body, that it may be cut into ten pieces, and every one will become a 

 new, perfect, living animal. This seems bordering on the vegetable 

 kingdom, in which it is common to propagate by means of slips from 

 the mature shrub. 



The J)olyp afiixes itself by its tail to various substances, and fre- 

 quently is a parasite to other animals, which it annoys, while benefited 

 itself by taking advantage of their locomotive powers : this is more 

 especially the case with the water-snail, on the body of which may 

 often be found the polyp. 



Dr. Koget, in his Bridgewater Treatise, copying Trembley, says : 

 " The position in which they appear to take most delight is that of 

 remaining suspended from the surface of the water by means of the 

 foot alone ; and this they effect in the following manner : When the 

 flat surface of the foot is exposed for a short time to the air, above the 



