210 CHARLES R. STOCKARD 



frequent occurrence of teratoma in the pelvic regions was in 

 line with any of these explanations. Misplaced blastomeres 

 might readily be in this portion of the body and twin inclusions 

 or partially deformed twin bodies are frequently connected with 

 the pelvic region. 



The parthenogenetic theory which has received considerable 

 support would necessitate the occurrence of all such formations 

 in close proximity to the gonads and therefore would practically 

 limit their occurrence to the pelvic region. It so happens, how- 

 ever, that teratomata occur with considerable frequency in the 

 head and neck regions. This is most difficult to explain on the 

 basis of a parthenogenetic origin. It might be possible, though 

 not so probable (for the blastomere theory), that misplaced 

 blastomeres arrested in the early egg might develop in such 

 cephalic positions. 



On the other hand, if teratoma arises from early twin inclusions, 

 one would, on the basis of our series and a general survey of 

 recorded double individuals, readily recognize that the head and 

 neck regions should be places of frequent occurrence for these 

 structures. The double specimens arrange themselves roughly 

 into two groups, the anterior duplicities or double-headed lot, 

 and the completely double specimens. 



Should the smaller components of the first group become 

 greatly inhibited and included within the larger components, we 

 should have the inclusions in the head region. Should these 

 then give rise to teratomata, such growths would not be expected 

 to contain tissues found in the caudal regions of the body, such, 

 for example, as nephric, gonadal, lower intestinal structures, 

 etc. The rather frequent occurrence of teratoma in the head 

 and neck would be what one would expect. 



The inclusion of the smaller component of the completely 

 double specmien would in most cases occur in the lower abdominal 

 region. This would account for the great frequency of pelvic 

 teratomata. Such teratomata in contrast to those of the neck 

 region, may be found to contain tissues characteristic of any 

 portion of the body, since these are inclusions of a possibly 

 complete twin and are not limited to structures of either the 



