PROFESSOR OWEN ON LIMULUS POLYPHEMUS. 193 



dorsal and smaller ventral chord. The dorsal division (PI. XXXV, fig. 2, d) soon 

 expands, and resolves itself into a fasciculus of nervules, which subdivide, and finally 

 supply or form the retinae of the lenses at the upper and hinder part of the compound 

 eye. The ventral, which is also the anterior division (id., v), is continued before expand- 

 ing and resolving into the plexus which supplies the retinae to the lenses at the lower 

 and forepart of the compound eye. 



" Gastric Nerves. — Two pairs of nerves arise posterior to the ocular pair. The 

 nerves of the first pair (n, 3, PI. XXXVI) pass forward, give filaments to the oesophagus 

 and stomach, and are continued on into the hepatic and ovarian substance at the fore- 

 part of the carapace. 



" First Epimeral Nerve. — The nerves of the second pair (on the outer side of the 

 symbol n, 4, PI. XXXVI) diverge, extend along the forepart of the anterior low and 

 simple apodeme (u), subdivide, and are lost in the tissues of that part of the segment ; 

 answering, in position, to the epimerals l of the type segment. The term ' epimeral' 

 will, accordingly, be given to this and the succeeding serially homologous nerves. 



" Second Epimeral Nerve. — A somewhat larger nerve rises immediately behind the 

 foregoing ; the pair ( Pi. XXXVI, n, 5) slightly diverge and ascend, when each second 

 epimeral nerve bifurcates. One branch coasts along the anterior apodeme, the other 

 inclines towards the interspace between that and the second more prominent apodeme, 

 supplies muscular fibres thence arising, and gives off a recurrent filament (n, G), trace- 

 able along the outer ends of the succeeding apodemes (n — vi, PI. XXXVI), at a little 

 distance from them, as far as the seventh epimeral nerve, where this begins to ramify. 



" Antennidar Nerve. — This nerve (n n, Pis. XXXIV and XXXV) rises from the 

 under part of the base of the brain {a, fig. 1, PI. XXXV), is rather larger than the 

 second epimeral nerve, and supplies the first small forcipated pair of limbs, the homo- 

 logue of the first, or inner pair of antennae in higher and more differentiated Crustaceans. 



" Two filamentary nerves rise from the interval between the antennular and antennal 

 nerves at the beginning of the lateral parts of the ring (shown in PI. XXXV). 



" Antennal Nerve. — This nerve {n, in) is more than twice the size of the antennular 

 one ; it supplies the second limb (PI. XXXV, in), which is sexually modified in the male 

 of Limulus polyphemus. This limb, forcipated like the rest in the female, is the homologue 

 of the outer and larger pair of antennae in higher Crustaceans ; and its origin is prae- or 

 supra-cesophageal in Limulus. 



" Third Epimeral Nerve. — From the dorsal aspect of the lateral part of the neural 

 ring rises the third ' epimeral nerve ' (n, 7, PI. XXXVI). It runs forward and outward 

 above the interspace between the second (ib., n) and third (in) apodemes, and is resolved 

 into a plexus of filaments beyond that interspace, which are lost in the glandular and 

 other tissues of that region. 



"Mandibular Nerve. — The third limb nerve (PI. XXXV, n, iv), of the same size as 

 1 Owen's ' Lectures on Invertebrata,' p. 298. 



