78 THE GERM-PLASM THEORY 



an Amphioxus, forms an entire and undivided 

 Amphioxus. And his reply is, " it is only necessary 

 to assume that the segmentation-cells, which 

 develop in the isolated condition as if they were 

 intact eggs, still contain the complete germ-plasm, 

 and that the differential segregation into groups 

 of determinants with dissimilar heredity tenden- 

 cies takes place later " (Vol. i. 406). 



Again, he is called upon to deal with the great 

 question of regeneration. The fresh-water hydra 

 can be cut up into almost any number of pieces, 

 and out of each one of them a new complete hydra 

 may arise. The same may be done with a little 

 moss known as Funaria hygrometrica, from every 

 minute fragment of which a new plant will arise. 

 Think how many willow- trees can be grown from 

 a single willow by means of cuttings ! Passing to 

 worms, Lumbriculus has been cut up into twenty- 

 six pieces each two millimetres in length, and 

 most of them formed new complete animals. A 

 much more highly organized animal, the water- 

 newt or triton, can regrow its limbs. Spallanzani 

 six times cut the legs off a single newt, and six 

 times the animal grew those limbs again. Weis- 

 mann admits that these cases certainly do not 

 afford any special evidence of its validity," i e., 

 the validity of his theory, "as an interpretation" 

 (xx. ii. 7), but he has his reply, for speaking of the 

 hydra, he says : 



" The animal's high regenerative capacity must, 

 therefore, depend on the fact that certain cells 

 of the ectoderm are equipped with the complete 



