Six embryos measuring 9–12 mm in greatest length have been shown by the writer to contain early splenic primordia in the left aspect of the dorsal mesogastrium. Their ovulation age is estimated to be 31–36 days. Temporal relations of splenic formation to conotruncus septation and division of the A‐V canal have been discussed. This last is divided before septation of the conotruncus is completed. The author has shown that early splenic primordia exist at the time of fusion of the A‐V canal cushions. At the same time there is initiation of pulmonary lobation, and there is a primitive gut mesentery.