130 



CARNEGIE INSTITUTION OF WASHINGTON. 



large nuniljcr of males. In one ease a Svild' Daphnia pulex, immediately 

 after having been brought under laboratory conditions, produced a large 

 prej^onderance of males. Some discarded Daphnia pulex in a neglected jar 

 long left standing in the laboratory produced males at a time when none of 

 the 18 Daphnia pulex lines receiving the usual laboratorj'^ treatment showed 

 any tendency to the production of sexual forms. The above were the cases 

 of the occurrences of sexual forms during the past year. The few earher 

 appearances of sex forms in my cultures were under similar circumstances." 



In the sex-intergrade stock similarly modified sex-ratios occurred 

 contemporaneously in the ofTspring of large numbers of mothers; but 

 whether this result is due to a similar change of environment acting 

 on all lines or to simultaneous mutation is uncertain. 



The following Unes of Cladocera are being bred in Dr. Banta's 

 laboratory: 



"(a) These 48 strains of 5 species of Cladocera have produced males in only a 

 few isolated instances and under the conditions in the laboratory have shown 

 no evidence of an innate sexual cycle which it is generally supposed exists in 

 Cladocera. Strains of four of these species have been reared for over 100 

 generations solely by parthenogenetic reproduction. One of these species 

 has been reared 169 generations and another over 200 generations, the former 

 for a period of more than four years and the latter for almost five years. If 

 sexual reproduction were necessary or a sexual cycle an innate necessary thing, 

 such ought long since to have becom.e manifest. 



"(6) In spite of this long-continued and uninterrupted parthenogenetic 

 reproduction these strains show no decrease in reproductive vigor. Tests 

 show that these strains have apparently as great virility and reproductive 

 capacity as 'wild' lines recently brought under laboratory conditions. 



"(c) These pure lines further serve as material on which to do additional work 

 on inheritance in parthenogenetic reproduction." 



SEX IN MUCORS. 



Dr. Blakeslee brings to this Station his problem on sexual differen- 

 tiation in the mucors upon which he has worked for many years; but in 

 adjusting himself to the new conditions he has not found time to work 

 on this topic. 



