Harris Hawthorne Wilder oSd 



to this hypothesis, which, in the light of our present knowledge, appears 

 to be not far from the truth, we may designate these two types respectively 

 as Fraternal and Duplicate, thus doing away with the misleading and in- 

 applicable terms " identical " and " homologous " as applied to the one 

 type, and furnishing a distingiiishing term for the other, which seems 

 thus far to have remained without a name/ 



Intra-uteeine Eelations. — As the discussion of the origin of these 

 two types of twins leads us to the consideration of the conditions which 

 obtain during early embryonic life, we naturally turn to the observations 

 furnished by obstetricians ; but this source, although supplying numerous 

 illuminating facts, is less valuable than it should be, owing to the fact 

 that medical men share the popular confusion noted above in regard to 

 twins and that, Avhile they record trustworthy details concerning placen- 

 tation and other relationships, they fail to correlate with these the neceS" 

 sary data concerning sex and general r-esemhlance, the last item of which 

 involves the following up of the case through several years of develop- 

 ment, a line of work hard to accomplish during active professional life. 

 The most noteworthy set of data covering these points are those tabulated 

 by 0. Sohultze, 97, who gives in the form of a classification the various 

 intra-uterine relationships which have been observed in twin births, with 

 suggested correlations of the type of twin produced in each case. As this 

 table is so essential to the present inquiry, I will transfer it in a some- 

 what abbreviated form, modifying its very accurate terminology to con- 

 form to that in more general use.^ 



Intra-uterine Eelationships in Twin Gestations. 



Case 7. — Two separate blastodermic vesicles with two decidufe reflexge 

 and two placentse. This case is probably one in which there are two sepa- 

 rate eggs, either from the same or from opposite oviducts, and implanted 



^ Strictly speaking, the word " fraternal " applies only to twins of the male 

 sex, since in Latin, as well as in English, there is no word which, like the 

 German " Geschwister," applies to sisters and brothers alike. The present 

 use of the word in question, however, corresponds to that of the English 

 masculine pronoun " he " in similar cases, and thus seems entirely warrant- 

 able. Pearson's term " Sibling " is correct in meaning, but is so rarely used 

 that I hesitate to employ it. 



* Schultze confines the term " Keimblase " (blastodermic vesicle) to the 

 blastula stage of the embryo, employing for the later stages, to which the 

 same term has been generally applied hitherto, the term " Fruchtblase." The 

 parts surrounding this and supplied by the uterine mucous membrane are 

 termed collectively " Fruchtkapsel," the free portion of which is the decidua 

 capsularis (decidua reflexa autt.). 



