June 2, 1905.] 



SCIENCE. 



tions it is concluded that generic and 

 specific characters are the result of differ- 

 ences in size and associations of chromo- 

 somes, and not to variations in numbers. 

 It is also thought that continuous variation 

 may be due to slight differences in size of 

 the chromosomes of the germ cells, while 

 discontinuous variation would be due to 

 alterations in the relations of chromosomes 

 to each other. 



Begeneration in Nudibranclis: C. M. Child, 



University of Chicago. 



Several species of feolids abundant in the 

 Pacific Grove region Avere used for experi- 

 ment. 



It was found that removal of a portion 

 of the body posterior to the middle was fol- 

 lowed by rapid regeneration. The larger 

 the portion removed the more rapid the 

 regeneration. 



The ganglionic mass is situated posterior 

 to the second pair of tentacles ; removal of 

 the whole head anterior to the ganglia was 

 followed by rapid and complete regenera- 

 tion. "When the ganglia were removed no 

 regeneration beyond healing of the wound 

 occurred, though the animals often lived 

 for two weeks. 



Eegeneration of posterior portions of the 

 body was less rapid in specimens from 

 which the head anterior to the ganglia had 

 been removed than in specimens with unin- 

 jured head. The specimens from which 

 the head region had been removed had lost 

 their principal sense organs, but still re- 

 tained the central nervous system intact. 

 They were much less active than specimens 

 with normal heads and the posterior parts 

 were consequently subjected in much less 

 degree to the conditions accompanying 

 functional activity of this region ; hence in 

 all probability the less rapid regeneration. 

 After the new head regenerated, posterior 

 regeneration in these pieces was fully as 

 rapid as in those with uninjured heads. 



Removal of other portions of the body such 

 as the lateral regions of the foot, etc., had 

 no effect upon the rapidity of posterior 

 regeneration. 



If the animals are not fed a marked re- 

 duction in size, often 50 per cent., occurs in 

 the course of two or three weeks. 



The Relation of the Degree of Injury to 



the Bate of Begeneration: Charles 



Zeleny, Indiana University. 



Two series of the crayfish, Camharus 

 propinquus, differing only in the degree of 

 injury which they had sustained, were com- 

 pared with regard to the rate of regenera- 

 tion of the right chela and the rate of 

 moulting. In one series, AA^, the right 

 chela was removed at its breaking joint. 

 In the other series, BBo, both chelae were 

 removed at their breaking joints and the 

 last two pairs of walking legs were like- 

 wise removed. Series AA2 comprised 36 

 individuals and series BB2 41 individuals. 



A comparison of the two series was made 

 95 days, 130 days and 153 days after the 

 operation. In each case the data show 

 very definitely that the series with the 

 greater injury molts sooner than the one 

 with the lesser injury and also regenerates 

 each of its two chelae more rapidly than 

 the latter regenerates its one removed chela. 



Experimental Evidence Concerning the 

 Production and the Preservation of Ac- 

 quired Characters : W. L. Tower, Uni- 

 versity of Chicago. 



Dominance ; a Potent Factor in the Extinc- 

 tion of Species: W. L. Tower, Univer- 

 sity of Chicago. Read by title only. 



The Origin and Distribution of Tropical 

 American Fresh-ioater Fish: C. H, 

 EiGENMANN, Indiana University. 



The Sequence of Organisms in a Protozoan 

 Culture and its Irreversihility : Amos W. 

 Peters, Zoological Laboratory, Univer- 

 sity of Illinois. 



