. Anatomy of the king crab (Limulus polyphemus, Latr.). Crabs. 44 connecting these with the suboesophageal mass, in Liniulus, giving the condition of that part of the nervous system, as in Scorpio and Juliis, as an ' annular centre,' the nerve- supply in Julus of two pairs of jointed appendages from the supera?sophageal lobes (Plate II, fig. 6), might be viewed in the following relation,—viz. that herein Idmulm manifested the more ' generalized type' of articulate structure, in which not only Arach- nidan but Myriapodal characters were associated with Crustaceous ones. But, in the development
. Anatomy of the king crab (Limulus polyphemus, Latr.). Crabs. 44 connecting these with the suboesophageal mass, in Liniulus, giving the condition of that part of the nervous system, as in Scorpio and Juliis, as an ' annular centre,' the nerve- supply in Julus of two pairs of jointed appendages from the supera?sophageal lobes (Plate II, fig. 6), might be viewed in the following relation,—viz. that herein Idmulm manifested the more ' generalized type' of articulate structure, in which not only Arach- nidan but Myriapodal characters were associated with Crustaceous ones. But, in the development of Limulus, the pleon or tail-spine (=pygidium) was the last to appear, and, at its first budding, looked like a ninth segment of the thoracetron. Packard, as .we have seen, speaks of indications therein (transitory, indeed) of segmentation of the crust; and such indications I have shown to be more strongly and lastingly given by the nervous system. After formifaction and the attractive and repellant forces have produced, in the germ- mass, the phenomena of segmentation and vegetative repetition (as manifested in the similar and parallel heaps of granules, like bricks for the building), the inherited influences seem to overrule the polaric ones and operate in differentiating and adaptive lines, speedily showing the embryo-form of a Limulus; which, like that of Astacus Jliwiatilis, Falcemon adspersns, Crangon maculosus, Eriphia spinifrons, Spiders, and, one may add, Cephalopods, goes straight to the goal of parental characters. There is no divergence to a larval form enjoying for a term an active independent life. There is no metamor- phosis, either naupHal, zoeal, or trilobitic. Other representative analogies, however, can be adduced, which are plain and intelligible. Arrest the development of Limulus at the tailless stage (figs. 7, 8), and one gets a ' Belinurus or a Prestwichia stadium' (fig. 17). Stay awhile in serving the warrant, and you have the short-tailed palaeozoic
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