RECORDS. 379 



this conclusion rests, let us ask how the idioplasm is to be con- 

 ceived. Some of those who have accepted the general concep- 

 tion of the idioplasm have endeavored to think of it as a very 

 complex but still single and homogeneous substance — the 

 frog's Ggg, for example, might be conceived as containing a 

 frog-determining substance, the human germ a man-determining 

 substance, and so on. The most recent researches are, how- 

 ever, continually strengthening the ground for a quite different 

 conception, indicating that the chromatin does not operate as a 

 simple substance, but is built into a complex fabric having a 

 definite architecture. We are not here concerned with the par- 

 ticular form of this conception developed by Weismann in his 

 well-known work on the Gcrni-plasm, and elsewhere. I am 

 referring to more recent results of observation and experiment 

 which are giving new and more concrete evidence that the 

 nucleus possesses a complex organization, and apparently one 

 that must be conceived as a kind of primary or original prefor- 

 mation, which bears a certain analogy to that assumed by Bon- 

 net, though quite distinct from it. 



We may perhaps most readily approach the grounds for this 

 conclusion by considering, first, an example of the indirect evi- 

 dence drawn from recent experiments on inheritance. I give a 

 single example, typical of a large number of known cases, of the 

 heredity of single or unit characters in the so-called Mendelian 

 inheritance. If pure gray mice be crossed with pure white 

 albino forms, the hybrid offspring are all gray without visible 

 trace of white. But if these gray hybrids be now paired with 

 each other, both parents being gray, approximately 25 per cent, 

 of their progeny are pure white without a trace of gray, and 

 they continue to produce pure white offspring thereafter. Many 

 similar cases are known, the same proportion of approximately 

 25 per cent, of the " recessive " character in the third generation 

 holding true, sometimes with great precision. What does this 

 prove ? First, that the white character is not really absent in 

 the gray hybrids but only masked or concealed — " recessive," 

 in Mendel's terminology ; secondly, that the latent white char- 

 acter may in the following generation be completely disentangled 



