THE PHILIPPINE 



Journal of Science 



B. Tropical Medicine 



Vol. XI MAY, 1916 No. 3 



ON THE DEVELOPMENT OF TWINS AND OTHER POLYEMBRYOS 

 WITH SPECIAL REFERENCE TO FOUR SETS OF DUCK 

 TWINS 1 



By Edward S. Ruth 



(From the Department of Anatomy, College of Medicine and Sufgery, 



University of the Philippines) 



THREE PLATES 



For centuries there has been a great deal of speculation 

 regarding the nature of the early development of twins and other 

 polyembryos. In a few of the lower invertebrate forms some 

 definite conclusions have been reached concerning polyembryony. 

 Twins, triplets, quadruplets, and even more than four organisms 

 have been produced experimentally from a single fertilized ovum. 



Experimental production of twins and other polyembryos in 

 mammals is impractical, and only a few theories have been estab- 

 lished. First, twins may possibly develop from one ovum by a 

 complete separation of the cells in the early stage of segmenta- 

 tion, possibly in the two- or four-cell stage. Secondly, two or 

 more ova may be contained in one Graafian follicle, all of which 

 become fertilized. Thirdly, an ovum sometimes contains more 

 than one nucleus, a multinucleated ovum which Stockel thinks 

 may occur either by fusion of two or more ova or by division of 

 the nucleus. Fourthly, an ovum may be fertilized following two 

 successive menstrual periods, this being known as superf etation. 



According to Mall,(i) the first workers (Valentine, (2) Lu- 

 chart,(3) and Muller(4)), while studying the formation of twins, 

 believed that the early primary change lies in the ovum or that 

 twins and other polyembryos develop by division of the embryo- 

 forming substance. Some of the later workers, who studied the 



' Received for publication May 10, 1916. 

 142020 109 



