REGENERATION AND DEATH 197 



ment of the animal kingdom, fresh illustrations of 

 the great importance of the young type of cells. 



We can learn the same thing from the study of 

 regeneration. The regenerative process depends to 

 a large extent upon partial differentiation, or even 

 upon its total absence. Regeneration is a most in- 

 teresting and wonderful process. I took pains only 

 this afternoon to look at that famous classic by 

 Trembley * on hydroids, or polyps as he called them. 

 The Fresh- Water Polyps, a book published in 1 744, 

 was well printed, and on such good paper that it 

 looks to-day almost like a new book. He per- 

 formed the curious experiment of cutting one of 

 these minute fresh-water polyps they are perhaps an 

 eighth of an inch long in two, and made the start- 

 ling discovery that each half of the polyp would make 

 up what the other half had deprived it of ; each half, 

 in other words, would become a new polyp. That 

 which was lost was regenerated. After him came a 

 series of yet more remarkable experiments by the 

 famous Italian naturalist, Spallanzani, one of the 

 masters of experimental research, and he discovered 

 that regeneration was a property which was not 

 peculiar by any means to polyps, but existed in the 



1 Memoire pour servir h V histoire d' un genre de polypes cT eau douce & 

 bras en forme des carnes, par A. Trembley, de la Societ-4 Roiale, a Leide, 

 MDCCXLIV., 410, pp. xvi., 324 ; 13 plates. A German translation by 

 J. A. E. Goeze was published at Quedlinburg in 1775. 



Abraham Trembley was born at Geneva, Switzerland, in 1700 and died there 

 in 1784. His famous experiments were made in Holland while he was engaged 

 as a tutor in the family of Count Bentiuck. 



