As central organs we have to note the brain-lobes and the longitudinal lateral cords which form one continuous unsegmented mass of fibrous and cellular nerve-tissue.
42) the six somites of the mesosoma are not fused to form a carapace at an early stage, and they are followed by three separately marked metasomatic somites; the other three somites of the metasoma have disappeared in Limulus, but are represented (From Lankester, loc. cit.) by the unsegmented prae-anal region.
The unsegmented dense chitinous sternal plate of the metasoma (XIII to XVIII) is not removed.
- Section through an early embryo of Limulus longispina, showing seven transverse divisions in the region of the unsegmented anterior carapace.