264 THE THEORY OF THE GENE 



the secondary characters of the female or at least fails 

 to develop those of the male. 



While most of the decapod Crustacea have male and 

 female sexes there are a few cases where both ovaries 

 and testes are present in one or in both sexes, and there 

 are a few cases where the young males may have large 

 egg-like cells in the testes. Several crayfish have also been 

 described that are sex intergrades, but no complete re- 

 versals are known.^ 



In Daphnians, and related forms, intersexual individ- 

 uals have been described by several observers (Kuttner, 

 Agar, Banta, etc.), but no complete reversals are known. 

 Sexton and Huxley have recently described some indi- 

 viduals of Gammarus that are called female intersexes, 

 which, ''on reaching maturity, more or less closely resem- 

 ble females but gradually come to resemble males more 

 and more nearly. ' ' 



Most of the barnacles are hermaphroditic. In some 

 genera there are, in addition to the large sessile hermaph- 

 rodites, minute complemental males, and there are a few 

 other species with sessile female individuals and comple- 

 mental males. The sessile individuals are generally sup- 

 posed to be true females, but Geoffrey Smith has sug- 

 gested that if a free-swimming larva becomes fixed it 

 grows to full size, passing through the male stage to be- 

 come a female, but if a free-swimming larva attaches 

 itself to a female it develops no further than the male 

 stage. This seems to mean no more than that the environ- 

 ment determines whether a potential individual develops 

 into a female or being arrested in its development be- 

 comes a male. 



The last case is similar to another in the gephyrean 

 worm, Bonellia, described by Baltzer. If a free-swimming 



1 See Faxon, Hay, Ortman, Andrews, Turner. 



