No. 577] SHOBTER ARTICLES AND DISCUSSION 



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into which Muller in common with the Hagedoorns 5 has fallen, 

 viz., (1) that individual pedigrees were not recorded in the 

 course of our selection experiments and (2) that no considerable 

 amount of inbreeding occurred in our work. 



It has been our invariable practise, upon recording the birth of 

 an animal and its grade, to record on the same line of the ledger 

 the record number of its mother and father. This enables one in 

 any particular case to trace back the pedigree to the very begin- 

 ning of our experiments. We have spent much time writing out 

 and studying individual pedigrees, but without discovering any 

 evidence of pure or prepotent lines or individuals, except in a 

 single case, that of our "mutant " series, the origin and complete 

 history of which we have described in detail. The pedigrees, 

 however, of our rats are on record available for study at any 

 time; their full publication would be a quite impossible under- 

 taking. 



That extensive and intensive inbreeding has occurred in our 

 experiments will be obvious when I state that all our animals 

 were descended from a very small initial stock, less than a 

 dozen individuals, that from the beginning we have made the 

 most extreme selections possible, mating like with like, never hesi- 

 tating to mate brother with sister, and putting aside for strict 

 brother-sister matings any litter of young which seemed espe- 

 cially promising. I may say that in no single case (except that 

 of the " mutant " series) have these " special " pens given us 

 advancement obviously greater or less than that of the general 

 selection series of which they formed a part. Nevertheless, we 

 are still continuing to follow them up and will later publish a 

 detailed account of them. Finally I would call attention to pp. 

 20 and 21 with Tables 48-49 of our full publication, in which 

 are described the hooded offspring of a single selected hooded 

 and a single wild rat. The hooded and the wild rat produced 

 several young resembling the latter, that is, not hooded; these 

 were mated inter se, brother with sister. Among the grand- 

 children (F 2 ) occurred the usual 25 per cent, of recessives, 

 hooded. Two males were selected from these and mated with 

 females of as nearly the same grade as were available. This 

 process was repeated through seven generations in succession. 

 Seven times animals of like grade were mated together, brother 



6 Zeit. f. ind. Abst. u. Vererbxingslehre, 11, p. 145. See also my reply in 



