DEVELOPMENT IN ECHIDNA 



19 



right primary-primordium, discovered in the 

 sections. 



In the following stages you will find, first of 



am 



>st 



Fig. 7a. — Echidna : Transverse Section of an Older 

 Embryo (Semon's Embryo No. 5), showing the 

 Primary - Primordia shifted in Medioventral 

 Direction, and the Skin Muscular Tissue. 



ma, Primary-primordia ; Am, the skin muscular tissue ; am, amniotic fold. 



all, in connection with the progressive develop- 

 ment of the body wall, that a shifting of the 

 primary-primordia, originally situated in the 



