Sentence:  By that date however, the final steps towards the true suspended ceiling had been taken -- from 1947 onwards, standard kits of parts existed from which could be assembled systems of translucent, louvered or <WSD>egg-crated</WSD> suspended ceilings with suitable provision for the downward diffusion of conditioned air, either through specialised outlets or (in the louvered versions) over the whole ceiling. 
Meaning of the word marked with <WSD> tags:  Having a texture with regular indentations similar to that of an egg carton or regular holes in a grid pattern; corrugated or latticed.