Sentence:  In all the cases which I have observed, the ciliated bands so characteristic of the pseudembryonic form have made their appearance before the rupture of the vitelline sac; and frequently the pseudembryo has become somewhat reniform, a depressed ciliated patch indicating the position of the <WSD>pseudostome</WSD>. 
Meaning of the word marked with <WSD> tags:  The oral opening on the pseudembryo of an echinoderm.