In this investigation we have attempted (1) to observe the occurrence and (2) to follow the behavior of mutations in parthenogenesis. We have found that mutations occur in parthenogenesis and that these mutant characters after their origin undergo further mutative changes.
(3) We have followed certain of these mutations through sexual reproduction. They behave as normal Mendelian characters and thus our studies on inheritance in parthenogenesis may be linked up with the very many other studies on inheritance of Mendelian characters.
I n h e r i t a n c e in p a r t h e n o genetic reproduction. For parthenogenetic reproduction our Cladocera are reared individually in wide-mouthed glass bottles, each containing about 75 c. c. of culture medium (a brei of stable manure). In parthenogenesis (at 20ยฐ C) they produce a generation each week from eggs which do not undergo chromatic reduction during the maturation process. This last fact is of especial interest since, because of it, segregation does not occur and all the parthenogenetic descendants of any individual should be genetically precisely alike e x c e p t a s a m u t a t i o n o c c u r s.
Five characters have been studied in parthenogenetic reproduction, two in Simocephalus exspinosus and three in D a p h ni a 1 on gi s p i n a. Changes in reactiveness to light and in the degree Qf sex intergradedness were studied in the former species.
Changes in reactiveness to light were studied by means of selection. This study has been published and it will suffice to say here that mu-