290 ILLINOIS ACADEMY OF SCIENCE 



ation. As wdtli most hypotheses regarding secondary 

 sexual characters his evidence is taken largely from 

 higher animals. 



Numerous investigations have shown that the develop- 

 ment of secondary sexual characters is directly asso- 

 ciated with the development of the gonads. In many 

 instances males deprived of the testes have failed to de- 

 velop characters peculiar to the male sex. Similarly, 

 it has been shown that old individuals after the close 

 of reproductive activity tend to acquire characters inter- 

 mediate between those characteristic of the two sexes. 

 Unfortunately, because of their endoparasitic habit, the 

 Acanthocephala do not lend themselves to experimental 

 investigations such as those of castration mentioned 

 above. However, in as much as all of the instances of 

 dimorphism cited among the Acanthocephala are re- 

 stricted to differences in development or relative size of 

 similar structures in the opposite sexes, it seems prob- 

 able that the physiological conditions accompanying the 

 development of the gonads are directly correlated with 

 the differences in general metabolic processes which con- 

 trol general body growth. 



Child (1915:350) has shown that fully formed eggs 

 have a relatively low rate of metabolism. Among the 

 Acanthocephala egg production is not a continuous pro- 

 cess. In the individual female the period of development 

 of the eggs is restricted to a single cycle for the gonad 

 becomes entirely used up in the production of the eggs. 

 Consequently the mature female grows considerably in 

 size after the period of egg formation has ceased. This 

 is probably due to the fact that food material during the 

 period of egg formation is largely utilized in that pro- 

 cess and at the close of that cycle becomes more generally 

 available for body growth. 



In contrast with this the male acanthocephalan con- 

 tinues to produce spermatozoa through an indefinite per- 

 iod of functional activity of the persistant gonads. It 

 seems probable that the continued development of 

 gametes utilizes available elaborated food at the ex- 

 pense of the farther growth of the body. Upon this 



