532 THE AMERICAN NATURALIST [Vol.XLVII 



this should prove to be the case the hypothesis here 

 offered would receive a striking support. A detailed 

 description of the life history of the parasite here dis- 

 cussed is in preparation and will no doubt soon appear 

 in print. 



The Peoblem of the Orientation of the Compound 

 Vesicle in the Uterus and the Origin of Pairs 

 One of the most striking facts that came to light in 

 the early stages of the present studies is that the vesicle 

 is distinctly a bilateral object and that this bilaterality is 

 ' strictly in accord with the bilaterality of the uterus. It 

 was noted that one pair of fetuses was attached to the 

 right and the other to the left placental disc. It was 

 furthermore discovered that this pairing is not merely 

 a mechanical adjustment of the fetuses to the shape of 

 the uterus, but involves resemblances in stage of develop- 

 ment, size and the minutiae of inherited peculiarities. To 

 explain this condition we offered the conjecture that each 



