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ILLINOIS ACADEMY OF SCIENCE 



observed. In immature specimens it is impossible to dis- 

 tinguish the sexes without observation of the essential 

 organs of reproduction. 



Plagiorhynchus formosus VanC. 



Fig. 1. Male. Fig. 2. Female. Both figures drawn to same 

 scale. 



Another extreme example of difference in length is 

 found in Meter opliis grandis (VanC), the female of 

 which is approximately five times as long as the male 

 (see figures 3 and 4) but only about one-third greater 

 in diameter of the body. 



Heteroplus grandis (VanC.) 



Fig. 3. Male. Fig. 4. Female. Both figures drawn to same 

 scale. 



No one has ever demonstrated the presence of cell di- 

 vision in other than germ cells in the body of an acantho- 

 cephalan after it has entered its definitive host. In addi- 

 tion to this the writer has shoAvn that in members of the 

 family Neoechinorhynchidae the number of cellular ele- 

 ments is fixed and in structures common to both sexes is 



