THEORY OF SEX-DIMORPHISM 85 



female characters appeared. Smith and Potts 

 are both of opinion that what happens is a 

 change of the metabolism of the crab on to 

 female lines. In Inachus, the putting on of 

 external feminine characters preceded the 

 appearance of the ovaries, so that the theory 

 of a specific secretion passing from the gonads 

 to the body is in this case excluded. 



Smith's theory has an important bearing 

 on the significance of sex and on the rfile 

 ascribed to internal secretions. Without going 

 into technicalities, let us seek to understand 

 more precisely what he means by saying that 

 the parasite disturbs the general metabolism 

 and that this affects the expressions of sex. 

 In a normal female crab the ripening ovary 

 takes up lutein and fat ; this seems to stimulate 

 the liver to make more, and to lessen another 

 of its functions, namely, making glycogen 

 (or animal starch) which is used in growth. 

 In the ripening female the blood becomes 

 progressively charged with fat and lutein, 

 and this might be described as the distinc- 

 tively feminine condition of the blood. Now 

 the roots of the Sacculina penetrating through 

 the male crab affect the metabolism just as 

 an ovary does in a female. They take up fat 

 and stimulate the liver to make more. The 

 glycogenic function is depressed, for there is 

 an absence of demand for glycogen, there 

 being no growing or moulting after the 

 Sacculina has protruded on the under side 

 of the crab (see Fig. 16). It has not been 

 shown that the male's blood is actually 

 charged with lutein and fat, but the liver is 

 always coloured with lutein, and so are the 



