No. 512] MALE CRAYFISH WITH FEMALE ORGANS 469 



external organs would develop at all without the internal 

 gonad can only be determined by future experiment, but 

 the abnormal eases above cited show that the external 

 organ may be formed without the gonad of that sex to 

 which the external organ ought to belong and make it 

 probable that the external organs and the gonads are so 

 independent that we need not suppose one leads to the 

 formation of the other. 



The sex of the crayfish is not merely the possession 

 of egg or sperm, but of something made evident in a 

 variety of places over the body, as sex organs that are 

 accompanied by the necessary reflexes and instincts to 

 use them. 



That the sex is rather intimately dependent upon func- 

 tion seems to be indicated by the occurrence of the two 

 forms of male, known as the first and second, which alter- 

 nate in such a way that at the breeding season the ex- 

 ternal organs of the male are perfect, while at another 

 time of year the same male has relapsed into a juvenile 

 state in which the sperm transfer organs are as they 

 were in youth and probably of little or no functional 

 value. These morphological changes are made possible 

 by the shedding of the shell and the growth of what is 

 practically a new organ. 



We have then some reason for supposing that back of 

 the visible sex organs there is some state or condition 

 of the organism that can at least modify the structure 

 of the sex organs. 



Nothing is known as to the origin of these gynandro- 

 morph crayfishes. But regarding the eggs as at first 

 able to make either male or female, or make more than 

 one individual under certain circumstances, the gynan- 

 dromorph may be looked at as a partial realization of 

 the entire set of possible organs. The causes may lie 

 in physiological states present at various stages of ontog- 

 eny. Where a whole species is gynandromorphic the 

 egg may be predestined in the ovary to produce a mix- 

 ture of organs. When only an occasional individual has 



