EMBRYONIC DETERMINATION IN THE ANNELID, SABELLARIA VULGARIS

Abstract

1. A simple method for the production of complete and partial exogastruæ in Sabellaria vulgaris is described. 2. In the complete exogastruæ, no internal gut is formed. In the partial exogastruæ there is no internal œsophagus, but the stomach and intestine develop normally. 3. Both the ectoderm and endoderm show complete self-differentiation in the exogastruæ, indicating that one layer exercises no inducing effect upon the other between six and forty-eight hours of development, from gastrulation to the well-developed trochophore.