8 JAS. p. HILL. 



and which connects the yolk- stalk with the inner surface of 

 the tubular umbilical stalk (fig. 4). In the upper part of the 

 umbilical stalk the vitelline vein becomes considerably 

 reduced in size, and is a much smaller vessel than the 

 allantoic vein. In this stage the vitelline vein is very re- 

 markably reduced as compared with the same vessel in 

 Stages C and D. The vitelline artery in the upper part of 

 the umbilical stalk is also a quite insignificant trunk, about 

 half the size of one of the allantoic arteries, although its 

 diameter is considerably greater as it courses over the yolk- 

 sac splanchnopleure. These facts are sufficient to show that 

 at this stage the yolk-sac vessels play a quite insignificant 

 part in the nutrition of the embryo as compared with their 

 functional importance in Stages C and D. 



The bilaminar omphalopleure calls for no special mention 

 here, beyond the remark that it composes the larger half of 

 the entire surface of the globular embryonic formation. 



Structural Details. 



The following account of the structural features of the 

 uterus and foetal membranes is made very brief, in view of 

 the close agreement of this stage with my previous Stage D. 

 In writing up the present paper I have had, after an interval 

 of a year, to carefully re-examine many of my old prepara- 

 tions, and compare them with those of this stage, with the 

 result that I am able to substantially confirm my previous 

 account. 



I. Uterus. — The serosa, muscularis, and corium present 

 essentially the same appearances as in Stage D. The uterine 

 glands are considerably enlarged, and lined by a low cubical 

 epithelium ; and very numerous blood-vessels occur in the 

 much attenuated interglandular connective tissue. 



(rt) Allantoic Placental Syncytium. — This has the 

 same average thickness as in Stage D, viz. '12 mm., and shows 

 no differences from that stage worthy of remark beyond the 

 fact that its capillary system is somewhat better developed, 



