Il6 THE OCEAN WORLD. 



There are learned men who have composed hundreds of volumes, 

 who have published whole libraries naturalists and physicists who 

 have written more than Voltaire ever penned, but whose names are 

 almost forgotten. On the other hand, there are some who have left 

 only two or three monographs, and yet their names will live for ever. 

 Of this number is A. Trembley. This writer published in 1744 a 

 " Memoir on the Fresh-water Polyp." In this little work he recorded 

 his observations on some of these animals of the smallest dimensions. 

 He limited himself even to two sets of experiments \ he turned the 

 fresh-water polyp outside in, and he multiplied it by cutting it up. 

 These experiments upon this little creature, which few persons had 

 seen, have sufficed to secure immortality to his name. Trembley was 

 tutor to the two sons of Count de Bentinck. He made his observa- 

 tions at the country-house of the Dutch nobleman, and he had, as he 

 assures us, " frequent occasion to satisfy himself, in the case of his 

 two pupils, that we can even in infancy taste the pleasures derivable 

 from the studies of Nature !" Let us earnestly hope that this 

 thought, uttered by a celebrated naturalist, who spoke only what 

 he knew himself, may remain engraved on the minds of our younger 

 readers. 



Trembley established by his observations, a thousand times repeated, 

 that Hydra viridis can be turned outside in as completely as a glove 

 may be, without injury to the animal, which a day or two after this 

 evolution resumes its ordinary functions. Such is the vitality of these 

 little beings, that what was once the outer surface soon fulfils all the 

 functions of a stomach, digesting its food, while the intestinal tube, 

 expanding its exterior, performs all the functions of an outer surface, 

 it absorbs and respires. But we shall leave Trembley to relate his very 

 remarkable experiments. 



" I attempted," he says, " for the first time to turn these polyps 

 inside out in the month of July, 1741, but unsuccessfully. I was 

 more successful the following year, having found an expedient which 

 was of easy execution. I began by giving a worm to the polyp, 

 and put it, when the stomach was well filled, into a little water 

 which filled the hollow of my left hand. I pressed it afterwards with 

 a gentle pinch towards the posterior extremities. In this manner I 

 pressed the worm which was in the stomach against the mouth of 

 the polyp, forcing it to open continuing the pinching pressure until 

 the worm was partly pressed out of the mouth. When the polyp was 

 in this state I conducted it gently out of the water, without damaging 

 it, and placed it upon the edge of my hand, which was simply mois- 

 tened in order that the polyp should not stick to it. I forced it to 



