Monoecism and Intersexuality 457 



mentioned above would suggest itself: the sex modifier in Strepto- 

 carpus and Solarium acts upon the flower bud before the determina- 

 tion of the pattern of a monoecious flower; while in Melandrium and 

 EcbaUium the X-Y system works only after the anlagen of the flower 

 parts have been determined. In favor of this solution is my work 

 (see II 2 C a) on the cytoplasmic effect upon the pigment-forming 

 process in Lijnuintria, where it was shown by a study of the pigmenta- 

 tion process in development that the cytoplasmic interaction with a 

 pair of alleles affects the speed of the process. 



d. The embryological side of the problem 



At this point we must return again to intersexuality in animals, 

 in order to show that complications exist, which make a kind of bridge 

 between monoecism and intersexuaHty by combining some features of 

 each in the same individual. The facts relate both to the genetic basis 

 and to developmental control of sexual differences. I have emphasized 

 repeatedly that the genie control of sexual differentiation works with 

 an alternative norm of reaction, meaning that a group of cells, which 

 may be so large as to include all cells, are able to develop in the 

 female or male way, according to the genetic situation. This includes 

 also the "short cut" of hormonic actions, which are genically con- 

 trolled. It includes also the corollary that the decision of the alterna- 

 tive norm of reaction may be brought about or superseded by genetic, 

 environmental, or hormonal action in proper experiments. 



To this basic solution we must now add that the morphological 

 basis for the developmental alternative is not simply a cell or group 

 of cells with the potency for alternative differentiation. Actually, in 

 animals we meet with two primary types. Some sexually different 

 organs are homologous in both sexes, which, in this instance means 

 development from the same primordia. Other sexually different organs 

 develop from different primordia. Examples of the first type are the 

 gonads and parts of the ducts in insects. Examples of the second type 

 are some parts of the ducts and external genitalia in insects which 

 are formed by different imaginal discs; the ducts in vertebrates, 

 developed from different anlagen (Miiller's and Woff's ducts); and 

 the vertebrate gonads developed from different parts of a primary 

 anlage (cortex and medulla). 



The results expected from this situation, in intersexuality, are 

 different accordingly. Intersexuality results in development first with 

 the chromosomal sex and later, after the turning point, with the 

 opposite sex, as proved for Lymantria ( Goldschmidt, 1916 ff.), Dro- 



