FETAL DEVELOPMENT 361 



and pancreas are developed from prolusions from the sides of the 

 duodenum. 



The bladder has been seen to be that part of the allantois 

 which is constricted off and remains in the body. 



The lungs are developed from the esophagus and at first lie 

 in the abdominal cavity; but the formation of the diaphragm 

 fixes them in the thorax. 



The kidneys are developed from the Wolman bodies. These 

 bodies are embryonic structures only. Each is a tube lying 

 parallel to the vertebral column on either side of it. This tube 

 consists of a collection of tubules, which unite to form a common 

 excretory duct. This duct joins the corresponding one from the 

 opposite side to empty into the alimentary canal opposite the 

 allantoic stalk. Outside the Wolman bodies are two other 

 ducts, the ducts of Miiller. They also enter the intestine. 



The Wolman body finally gives place to the kidney, from 

 which the ureter is developed. 



In the female the ducts of Miiller become the tube, uterus and 

 vagina. In the male they atrophy. 



Just behind the Wolman bodies are developed the ovaries 

 or the testes, as the case may be. 



The development of a few of the organs has thus been simply 

 referred to. 



Satisfactory explanation of these procedures can be given 

 only in extended works on embryology, and this section may be 

 closed with the subjoined table of development, which is abbre- 

 viated from one by Heisler : 



First Week. Segmentation and passage of ovum to uterus. 



Second Week. Ovum in uterus. Decidua reflexa present. 

 Entoderm and ectoderm layers formed also mesoderm. Em- 

 bryonal area, primitive streak in primitive groove. Chorion 

 and villi. Amnion folds. Umbilical vesicle partly formed. 



