208 THE PERPETUATION OF ADAPTATIONS 



came first, but the hen gradually evolved from generalized an- 

 cestral forms quite dissimilar from the modern fowl. How were 

 the successive changes or variations impressed on the egg, until 

 such changes became normal to the modern types? 



D. SOMATIC AND GERM PLASM 



The old enigma has been partly solved through the experi- 

 mental method in modern biology. The full solution is indeed 

 far from reached, but the key apparently has been found. As 

 usual in science, imagination led the way in the search for this 

 key, which is now generally believed to be bound up in the con- 

 ception of the germ plasm as outlined in a series of hypotheses 

 by Darwin, Dalton, Spencer, Nageli, and especially by Weis- 

 mann in his famous essays on Heredity. According to Weis- 

 mann's conception, our lobster, like all animals, is made up of 

 two kinds of protoplasm, somatic plasm and germ plasm. The 

 somatic plasm forms the structures of the individual, including 

 all of the systems of nutrition and relation; the germ plasm, in 

 the female, is confined to the eggs and to the endothelium from 

 which eggs are formed, and in the male, to the sperm cells and to 

 the endothelium from which sperm cells are derived. The so- 

 matic plasm wears out and ultimately dies from old age, but the 

 germ plasm is handed down and continues to live in generation 

 after generation of descendants. The individual thus is a 

 nurse or carrier of the potentially immortal germ plasm; his 

 inheritance comes not from the somatic protoplasm of either 

 parent, but from the germ plasm of both, and here is the secret 

 of the conformity to type the race is preserved in the germ 

 plasm, and the race changes with changes in the germ plasm. 



The development of this idea forms one of the most interesting 

 chapters in the history of biological science. While highly specu- 

 lative, especially at the outset, it was nevertheless developed 

 on a basis of facts. These facts are connected with the phenom- 

 ena of mitosis or cell division, which were worked out by many 

 different observers during the two decades from 1870 to 1890. 

 It was found that every characteristic type of animal or plant cell 

 reproduces its like by cell division, and that the characteristic 



