Different Types of Sex Determination 467 



genes, producing only a few sons; (5) allelogenes, meaning females 

 which produce sometimes only daughters, sometimes (in different 

 egg batches) only sons; (6) mixed females, meaning amphogene off- 

 spring, though the mother is derived from a monogene 9 ; their grand- 

 daughters may again be monogene. De Lattin finds in Cyclisticus the 

 same classes, except for no. 5. While Vandel's incomplete monogenes 

 contain relatively high percentages of exceptions, de Lattin uses the 

 term only when few exceptions are found. 



The main facts on heredity in Vandel's experiments are as follows. 

 Amphogene females with males of amphogene origin produce half 

 daughters, half sons. Females of thelygene origin crossed with any 

 kind of male produce only monogene daughters. Thelygene females 

 produce either only thelygene females, or arrhenogene females, or 

 both. Exceptional females, daughters of an arrhenogene mother, have 

 preponderantly arrhenogene daughters, but occasionally also thely- 

 gene or mixed (no. 6) daughters. Allelogenes (no. 5) sometimes have 

 only arrhenogene daughters, sometimes both arrhenogene and thely- 

 gene ones. "Mixed" females (no. 6) may have arrhenogene, or 

 preponderantly thelygene, or both types of daughters. All these facts 

 agree with Vandel's explanation of directed meiotic division in female 

 heterogamety (the possibility of which had been proved by Seiler in 

 Talaeporia) and a cytoplasmic control of this (known to exist in 

 aphids ) . 



De Lattin's main objections to Vandel's theory are as follows. ( 1 ) 

 No female heterogamety is proved cytologically or genetically, that is, 

 by sex-linked inheritance. This means very little. In Lymantria dispar 

 the XY group is cytologically not discernible, and no sex-linked mu- 

 tants are known. But its cousin L. monacha has cytological differences 

 of the sexes (Seiler and Haniel, 1921) and also the correct case of 

 sex-hnked heredity ( Goldschmidt, 1921a). (2) In the offspring of 

 monogenic females, amphogenic females occasionally appear. How- 

 ever, there is no reason why the cytoplasmic control mechanism 

 should not be susceptible to occasional genetic or environmental modi- 

 fication. Actually we would be surprised if the directive mechanism 

 always acted like clockwork. (3) Arrhenogenic females are derived 

 frequently from thelygenic mothers, actually as half or more of the 

 daughters. Thus the cytoplasmic feature which is assumed to con- 

 trol directed meiosis cannot control the alternative, thelygene-arrheno- 

 gene. This difficulty would not be hard to overcome. If the cytoplasmic 

 factor decides that all eggs of a given female are monogene (i.e., 

 have a directed meiosis), other environmental or genetic modifiers 



