324 WILLIAM PATTEN. 



nerves to the first hind-brain neuromere, that supplying the 

 chel« is much the largest. We shall call it the neural or 

 pedal nerve; it undoubtedly corresponds to the sensory 

 roots of the abdominal segments, and agrees with them in 

 being a mixed motor and sensory nerve, in containing two 

 kinds of nerve-tubes, and in having at its base a ganglionic 

 swelling that we shall call the neural ganglion (Figs. 1 and 

 3, n. g.). The latter is serially homologous with the spinal 

 ganglia, as shown by its development from the neural crest ; 

 but it differs from them in being very much larger, in having 

 the ganglion-cells arranged upon the surface of the nerve- 

 root, and in being more intimately fused with the nerve-cord. 

 In Limulus there are at the base of the pedal nerves similar 

 swellings ; they are here more clearly ganglia of pedal nerves, 

 because they are more independent of the nerve-cord than in 

 Scorpio (Fig. 10, g. n^.). 



In Scorpions about ready to hatch, a short distance beyond 

 the neural ganglion is a purely sensory and richly ganglio- 

 nated coxal nerve; it is distributed to a number of sense- 

 organs on the median basal side of the legs; one of these organs 

 is very much larger than the rest, and from it is split off a very 

 large coxal ganglion (Fig. 8, cx.g.oxiA. cx.n.). Each of 

 the sense-buds {s.b.) also gives rise to one or more ganglion-cells, 

 which pass into the nerve that supplies the bud. There is a 

 similar set of coxal sense-organs in the spiny mandible-like 

 swellings in the coxal joints of Limulus. 



The main nerve is continued beyond the coxal nerve into 

 the chelae. Near the base of the chelae it expands into a 

 ganglionic swelling, formed by an inward proliferation from a 

 true segmental sense-organ ( s. s. o.). 



The exact fate of the coxal and segmental ganglia I have 

 not been able to determine. The large coxal sense-organ 

 seems to disappear, but the ganglion produced by it wanders 

 inward, forming a swelling on the coxal nerve. The segmental 

 sense-organ also disappears, and its ganglion probably unites 

 with the coxal ganglion. At any rate in the adult, I find a large 

 lateral ganglion united by several branches not only with 



