208 



POULTRY DISEASES 



atresia, imperforate anus, or other natural openings may re- 

 sult; a])normal position of viscera, a failure of the closure of 

 the abdominal or thoracic plates may take place. 



The germ or em])ryo is first developed as a manifold mcm- 

 brnnous expansion, the free margins of which incline towards 

 each other, and eventually meet to form two cavities. A 

 failure to meet results in malformation. Fusion of parts may 

 also take place. 



Those malformations in which there are supernumerary 

 parts or duplications of almost an entire body are sometimes 

 called composite or compound malformations and monsters. 



Hermaphroditism is a com- 

 plete duplication of both male 

 and female genital organs; 

 i. e., a single individual pos- 

 sessing both male and female 

 genital organs. Pseudo-her- 

 maphroditism is a condition 

 in which the duplication is 

 only partial. It is desirable 

 that more scientific observa- 

 tions be made along these 

 lines, in birds, and recorded. 



The double-yoked eggs, in 

 cases where two ova have 

 been delivered into the ovi- 

 duct at the same time, and 

 both being surrounded by al- 

 bumen and finally one shell, 

 have been supposed to pro- 

 duce double monsters, but 

 there is a scientific record in 

 which eighty such eggs were 

 incubated (all from the do- 

 mestic fowl J and in each sep- 

 arate twins were produced, 

 in some both males, in others 

 females, and in others one 

 of each sex. In one case out 

 single chick and the other a 



Fig. 72,. Polymelus (natural size). 

 A. the two supernumerary legs. 



of the eighty one yolk developed a 

 double monster. 



Thompson made a study of a double embryo 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 blastodermic mem- 

 brane proceeding from a single vitellus and vitelline membrane. 

 This same work has been corroborated by others so fortunate as to 

 find these monstrosities in early stages of development. 



Comjjound monsters lu'oceed from single germs which have sub- 

 sequently undergone different degrees of dichotomy. 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 



