The literature on the pathologic structure of the teratoma is in a most unsatisfactory state. On a recent occasion three pathologists were questioned as to the elements necessarily present in a tumor to admit it to classification as a teratoma. Each presented different criteria. The literature reveals a similar divergence of opinion, and the confusion is evidenced further by the number of theories that have been advanced by authors to explain the origin of such a tumor. To enter into a discussion of these subjects is beyond the scope of this paper, but the studies presented here strongly suggest that a teratoma arises as a misplaced blastomere. The more nearly totipotent the cell, the more differentiated will be the tumor when it grows.
Recognizing fully the objections to this theory, we believe that it still remains the most logical explanation of parasitic monsters and teratomas. By following this reasoning, teratomas