VARIOUS KINDS OF HUMAN TWINS ii 



of monozygotic twins. Frequently this evidence is lack- 

 ing in very essential points. Sometimes, for example, the 

 sex is not mentioned, and never, so far as I am aware, is 

 there information about the number of corpora lutea pres- 

 ent. The importance of the latter data cannot be over- 

 emphasized in this connection; a knowledge of whether 

 one or more corpora lutea are present would furnish a 

 crucial test of the number of ova concerned in a given 

 pregnancy. In not a single case of human multiple 

 births, so far as I am aware, has the number of corpora 

 lutea been noted. The reason for this is obvious: to 

 secure this information would require an operation dur- 

 ing pregnancy. It seems quite probable, however, that 

 post-mortem examinations of pregnant women, and of 

 those dying after abdominal operations or during par- 

 turition, might serve to give occasionally just the kind 

 of information that we must have in order to prove the 

 existence of monozygotic twinning in man. I would 

 therefore urge upon surgeons and obstetricians the im- 

 portance of collecting information as to the corpora 

 lutea whenever opportunity arises. 



Although data as to intra-uterine relations are incom- 

 plete and inconclusive, they form the only really direct 

 evidence now available on the mode of twinning in man. 

 The most reliable collection of such data is that of 

 0. Schultze.' He grouped his types into four catego- 

 ries which have been given by Wilder,^ together with 

 the latter's comments, as follows: 



Case I. — ^Two separate blastodermic vesicles with two decid- 

 uous reflexae and two placentae. This case is probably one in 



' O. Schultze, Leipzig, 1897. 



= H. H. Wilder, American Journal of Anatomy, III (1904). 



