234 THE BIOLOGY OF BIRDS 



which are first male and then female in the course of their 

 individual life. Thus according to Mr. J. T. Cunningham 

 and Nansen the explorer, who served his scientific apprentice- 

 ship as a zoologist, the glutinous hag {Myxine glutinosa), a 

 strange antiquity of a creature which lives in deep water in 

 the North Sea and sometimes bores into fishes caught on 

 the fishermen's deep-water lines, is one of these first- male- 

 and-then-female animals. In technical language, it illus- 

 trates protandrous dichogamy. 



Then there is the remarkable fact that a male shore-crab 

 which has its constitution altered and its testes destroyed by 

 Sacculina or some related parasite begins to put on feminine 

 and female characters. The abdomen broadens, its 

 appendages change towards the feminine type, and eggs may 

 be produced. Using the terminology of " The Evolution of 

 Sex," Geoffrey Smith said of the change in the constitution 

 of the male crab : " This adaptive regulation consists in the 

 production of at least a partially female condition of meta- 

 bolism as opposed to the wholly male condition, the female 

 condition being preponderantly anabolic or conservative, as 

 opposed to the katabolic male condition, and by this change 

 from a kataboUc to a more anabolic condition the animal 

 can withstand better the drain on its system increased by the 

 parasite." 



Another useful consideration is that the distinction 

 between male and female is not always clear-cut, for in types 

 so different as water-flea, moth, and pigeon, the occurrence of 

 inter-sex individuals is well known. 



Experiments on altering the sex of such larvae as tadpoles 

 and caterpillars by alterations of nurture have not been con- 

 clusive because the experimenters have not paid sufficient 

 attention to differential mortality. Yung found that tad- 

 poles, which normally develop into about 57 females to 

 43 males, yielded, when fed with beef, fish, and frog-flesh, 

 respectively 78, 81, and 92 females in the hundred. But 

 this is inconclusive until we know precisely how many larvae 

 died, and how many of these showed that they were going to 

 become males. 



