422 Duplicate Twins and Double Monsters 



IV. — Under the head of superfluity (the " monstra in excessu " of 

 the older writers) may be grouped the theories of several investigators 

 that see a cause for compound monsters in an excess of some of the ele- 

 ments of the original germ. Thus 0. and R. Hertwig, having suggested 

 as a working hypothesis that such cases are the- result of polyspermy, at- 

 tempted to develop double monsters from the eggs of sea-urchins into 

 which more than one spermatozoon had been introduced. The results 

 in this case were wholly negative. 



Wiedemann, 94, finds the superfluous material in both the male and 

 female elements and believes that compound monsters arise from the 

 presence of two germinal vesicles on a single yolk, each fertilized by a 

 separate spermatozoon. The great irritation produced by the two sper- 

 matozoa on the single egg occasions contractions which tend to draw the 

 two vesicles together. When there is protoplasm enough for two good 

 blastoderms they remain separate, and produce " die sogennante eineiige 

 Zwillinge ; " when not, a compound monster is the result. 



Considerable apparent support has been given to theories like the 

 foregoing by the discovery in the ovaries of various mammals, and recently 

 in man also, of primordial eggs with two nuclei, and of follicles enclosing 

 two eggs, and an interesting discussion was begun by v. Franque, 98, 

 and taken up by others (see Bibliography, IV), with the final conclusion 

 that the mature result of such phenomena is always two separate eggs, 

 although they may be discharged at one time, even from the same 

 Graafian follicle. There seems to be no reason why those eggs should 

 produce compound monsters, or even duplicate twins, since they must 

 be fertilized by different spermatozoa, but that fraternal twins may 

 often, if not always, result in this way seems probable. 



A theory which is in some ways the counterpart of that of a double egg 

 is the one recently suggested by Broman, 02, and based upon the occur- 

 rence of various forms of double and otherwise compound (" atypische ") 

 spermatozoa in man. Of these he figures a large number of forms and 

 comes to the conclusion that " die zweischwanzigen Spermien fiir die 

 Entstehung eineiiger Zwillinge wahrscheinlich eine grosse Rolle spielen 

 konnen. In derselben Weise konnen wahrscheinlich die drei- oder 

 vierschwanzigen Spermien zu eineiigen Driliingen resp. eineiigen Vier- 

 lingen Anlass geben" (loc. cit., p. 526). 



This theory he extends to double monsters because of the existence 

 of all transitional stages and concludes, if we accept the above conclu- 

 sions " dass wir auch fur die Genese der Doppelmonstra den atypischen 

 Spermien eine mogliche Bedeutung zuerkennen miissen." 



