MALFORMATIONS 



177 



both male and female genital organs. Pseudo-herma- 

 phroditism isa condition in which the duplication is only- 

 partial. It is desirable that more scientific observations be 

 made along these lines, in birds, and recorded. 



The double-yolked eggs, in cases where two ova have been 

 delivered into the oviduct at the same time, and both being 

 surrounded by albumen and finally one shell, have been sup- 

 posed to produce double monsters, but there is a scientific 

 record in which eighty such eggs were incubated (all from 

 the domestic fowl) and in each separate twins were pro- 

 duced, in some both males, in others females, and in others 

 one of each sex. In one case out of the eighty one yolk 

 developed a single 

 chick and the other a 

 double monster. 



Thompson made a 

 study of a double em- 

 bryo in the egg of a 

 goose, which had been 

 incubated five days. 

 This study showed a 

 double primitive trace 

 is actually formed on a 

 single b 1 a s t o d ermic 

 membrane proceeding a 

 single vitellus and vitel- 

 line membrane. This 

 same work has been 

 corroborated by others 

 so fortunate as to find 

 these monstrosities in 

 early stages of develop- 

 ment. 



Compound monsters 

 proceed from single 

 germs which have sub- 

 s e q u e n tly undergone 

 different degrees of 

 dichrotomy. They are 



governed in their development by certain fixed and invariable 

 laws among which are unity of sex, homologous fusion and 

 bilateral symmetry. In each case there is single sexuality. 



The various forms of duplex development are determined 

 by the extent to which the primitive trace is cleft, and also 

 by the limitations of the dichotomy to the cephalic or caudal 

 extremity of the neural axis. Either or both extremities may 

 become bifid. The cephalic or head extremity may become 

 bifid alone and a double head, or still further bifid and the 

 posterior extremities single or the posterior extremity be- 

 come bifid and the anterior single. 



Figs. 55 and 56 illustrates a duplication of the legs. The 

 rudimentary legs are perfect, but not so well developed as the 

 other two. This is polymelus. 



Fig. 56. Polymelus (natural size) 

 A, The two supernumerary legs. 



