The sporulation and crystal development of B. thuringiensis serotype H-14 was described for a wild spore- and crystal-forming strain and for a mutant crystal but non-spore-forming strain. The special nature of B. t. israelensis consisted in the composite structure of the crystal, made of a number of components differing in size, shape and electron density. The components were formed in a single inclusion or sometimes separately inside the same bacterial cell.