272 LILIAN SHELDON. 



Summary of Dates of Embryos which are figured in 

 this paper and the previous one (4). 



Previous paper (4) : 



Figs. 1 — 10. — December. Figs. 11 — 20. — April. Figs. 

 21a, b, c— July. Fig. 22.— July. Fig. 23.— December. 

 Fig. 24.— December. Fig. 25.— July. Fig. 26.— July. 



This paper : 



Figs. 1—9. — January. Fig. 10. — July. Fig. 11. — July. 



Thus, speaking generally, the ages of the embryos received 

 in the various months are : 



December. — Stages from unsegmented ova up to that 

 at which nuclei were present at intervals just beneath the 

 surface round about half the ovum. 



January. — From late segmentation up to gastrula stage. 



April. — Two embryos showing the beginning of the for- 

 mation of the blastoderm, and also several stages with ecto- 

 dermal yolk. 



July. — Stages in which the appendages are being formed 

 up to embryos which were ready for birth. There were also 

 newly-born young. 



Conclusion arrived at as to Time of Development. 



Probably the ova pass from the ovary into the uterus in 

 December, and the young are born in July, the development 

 thus occupying a period of about eight months. 



This, though apparently usually the case, cannot be universal 

 since in each lot there were one or two females which con- 

 tained embryos ready for birth, and also the embryos in one 

 female vary somewhat in age. 



This statement as to the period of gestation has already 

 been made by Mr. Sedgwick (2). 



