5 



In these various ways room for the intestines is obtained 

 in the abdominal coelom. 



The cavity of the umbiHcal cord is obviously very much 

 larger, in proportion to the abdominal cavity, in the younger 

 than in the older embryos (Figs, i, 2,3,4, S)- Its cavity 

 increases in size up to the time that the intestines leave it, 

 which would correspond to an embryo of from 20 to 30 milli- 

 metres in length. It then steadily atrophies until its cavity 

 is practically obliterated. The obliteration of this cavity is 

 due to a thickening (i.e., to an increase of the mesenchymal 

 tissue) of the somatopleure, which forms its walls, as well as 

 to a distinct contraction of the walls themselves (Figs. I, 2, 

 3, 4, and 5). 



The intestines enter the ccelom proper by growth. 



Space for their occupancy has been provided for them in 

 the different ways already enumerated, and their natural 

 growth or development takes them there. 



At first this seems to be a most disappointing, a most un- 

 satisfactory conclusion. One might like to have them pulled 

 in by their mesentery or pushed in by the union of the soma- 

 topleure, but I can find no evidence either in my sections or 

 dissections of anything of this kind taking place. 



There is no reason why the mesentery should have the 

 power of contraction, and surely if the closure of the walls 

 of the cord exerted any pressure upon them one would expect 

 to find the walls furrowed and grooved, after the manner of 

 the liver, which seems to keep them in the cavity of the cord 

 (Fig. I). 



There are several phenomena of this same kind in the 

 human body — examples of migration by growth. I will 

 mention only one — the descent of the testicle. No one 

 to-day believes that the mesorchium drags the testicle to the 

 scrotum. It may possibly be its guide, but it is not believed 

 to have the power of placing it there. The testicle reaches 

 its destination by growth ; and by this same process, when 

 the abdominal cavity is ready to receive them, the intestines 

 enter it, possibly also guided by their mesentery. 



The definite order of entrance of the intestines is depend- 

 ent upon the vitelline vessels. 



