AND EMBRYOLOGY OF LIMULUS. 43 



Fi^. 7. Section through an advanced larva showing tlie origin of a pair of liver duets from the intestines 

 [int'], and a single primitive liver-duct [Id], of which there are two pairs ; ht, heart ; gn, a pair of nerves sent 

 from the ganglion [^] to each second gnathopod. 



Fig. 8. Section of an ovarian tube, with the ovarian follicles on the side ; 8a, another section showing the 

 cell-eggs. 



Plate V. 



Fig. 1. Section through the vertical folds or teeth of the fore part of the crop or proventriculus ; m, mus- 

 cular layer ; pe, pavement epithelium ; ce, columnar epithelium ; ch, chitinous layer. 



Fig. 2. The central tooth of Fig. 1 magnified ; X ^ A; lettering as before. 



Fig. 3. Columnar epithelium from section of end of the oesophagus. 



Fig. 4. Nucleated cells and fibres of the pavement epithelium of intestine ; X J B ; 4^, the same somewhat 

 enlarged. 



Fig. 5. Section from posterior part of the oesophagus, showing the chitinous layer [cA] ; the empty 

 spaces in the lobes surrounded by columnar epithelium [ce ]; the pavement epithelium [/>e] supporting the 

 former. 



Fig. 6. Pavement epithelium of rectal folds. 



Fig. 7, 7a. Section of stomach of larva where the chitinous lining is absent, showing the irregularity of the 

 epithelium. 



Fig. 8. Section through an advanced larval Liraulus, the figure indicating only the portion lying under 

 the central lobe ; ht, heart ; pr, proventriculus ; oe, oesophagus ; g, first pair of ganglia, the oesophageal ring 

 not yet being consolidated ; gn, nerve to the first gnathopod [gp'\, demonstrating that the brain does not 

 supply the nerves to the first pair of feet ; ct, connective tissue, the neurilemma not yet formed. 



Fig. 9. Section of inner part of the proventriculus showing the larger teeth [<] alternating with the 

 smaller ones [<] ; X J A. 



Fig. 10. Section through the oesophagus ; X J A. 



Fig. 11. Another section of the same. 



Fig. 12. Section through the simple eye or ocellus of Limulus ; 3, third layer of the integument, clear and 

 laminated ; X J A ; 2, second layer of integument finely granulated and laminated ; pc, pore canals filled 

 with connective tissue [c<] ; cl, corneal lens ; h, cup-shaped depression in the base of the corneal lens. 



Fig. 13. Another section of an ocellus more enlarged; lettering as in fig. 12. 



Fig. 14. Section through an ocellus showing the relations of the ocellar nerve and its branches [ocn'] ; 

 1, first and outer clear layer of the convex cornea; 2, second layer, finely laminated; 3, third, clear layer, 

 with a few laminag ; rt, pigment layer in retina ; A, hyjjodermis, of which the retina is a modification ; cl, 

 corneal lens ; ct, connective tissue. 



Plate VI. 



Fig. 1. Section through the entire compound eye of Limulus, stained with picro-carmine, showing the 

 relations of the cornea and corneal lenses and retina to the branches of the optic nerve ; cor, cornea ; 1, outer 

 clear, 2, middle laminated, and 3, inner clear portion of the chitinous cornea, seen to extend into the integu- 

 ment ; pc, pore or nutritive canals filled with connective tissue ; cl, corneal lenses ; rt, retina ; hg, hypodermis, 

 of which the retina is a modification. Below is the mass of connective tissue cells [c<], through which the 

 tortuous branches of the optic nerve pass and impinge on the ends of the conical corneal lenses ; owing to the 

 tortuous course of the nerve-fibres, they appear not to be continuous in the thin section of which this is a 

 drawing, ov, ovary with cell eggs ; ar, two arterial twigs ; I, two liver tubes ; ict, inner, darker brown con- 

 nective tissue of the interior of the cephalothorax. 



Fig. 2. Sections of corneal lenses in the middle of the eye ; the retina has been removed by acid ; cl, 

 corneal Icnse : h, cup-shaped depression in base of lens ; 2a, the same from near the periphery of the eye, 

 where the corneal lenses are longer and more oblique directed inwards towards the middle of the eye. 



Fig. 3. Epithelium of the retina ai-ouad the end of a cone ; rhab, rhabdom ; i-cl, retinal cells. 



Fig. 4. Section of two retinulas, with the rhabdom [rhab'] in the centre; X i A; 4a, a retinula [ret] 

 9d with acid to show the twelve cells into each of which a ray of the rhabdom projects ; X i B. 



