50 THE PHYSIOLOGY OF TWINNING 



situs inversus viscerum, there is no disagreement between 

 Gemmill and his followers and myself, but I cannot 

 accept their theory of the origin of conjoined twins, 

 which are really much commoner in fishes than are 

 separate twins and have excited much more comment 

 and interest than the latter. The next chapter is to be 

 devoted exclusively to conjoined twins or true double 

 monsters, their causes, and mode of origin. 



