44 A. S. PACKARD, JR., ON THE ANATOMY 



Fig. 5. Section of soft parts of ocellus of Limulus, showing the subdivisions and mode of termination of 

 one branch of the ocellar nerve [ow] ; the branches are enveloped in connective tissue [ci]. The section 

 passes on one side of the corneal lens. 



Fig. 6. Optical section of corneal lenses of Limulus, as seen through the transparent cornea, showing 

 their slightly hexagonal appearance ; X 50 diameters. 



Fig. 7. Artificial section through the eye of Asaphus, a trilobite, to show the close similarity to the cor- 

 neal lenses of Limulus ; X ^ B eye-piece. 



Fig. 8. Longitudinal section through the eye of Asaphus showing the corneal lenses ; X ^ A. (Com- 

 pare with Fig. 1, 2, 2a, the corneal lenses of Limulus.) 



Fig. 9. Longitudinal section through the eye of Asaphus gigas; cl, corneal lenses; pc, pore canal; rt? 

 probable indications of the upper edge of the retina? 



Fig. 10. Section of part of the cornea of an Asaphus gigas which has been broken, showing several 

 entire corneal lenses side by side. 



Fig. 11. Section through one side of oesophageal ring passing through the nerve to one of the gnathopods 

 or cephalothoracic feet; nl, neurilemma; sp, space between neurilemma and the ganglion; nb, small 

 nucleogenous bodies at top of section or upper side of oesophageal ring ; Igc, longitudinal group of large 

 ganglion cells, extending along the outside of the oesophageal ring; gnn, gnathopodal nerve ; magnified 30 

 diameters. 



Fig. 11a. A large ganglion ceU \lgc], surrounded by smaller bipolar ganglion cells, magnified 224 

 diameters. 



Fig. 12. Section through second abdominal ganglion, n, nerve to one of the abdominal feet ; fa, fibres of 

 central nerves ; Igc, layer of large ganglion cells and nerve fibres arising from them ; x 30 diam. 



Fig. 13. Section through the same ganglion showing origin of nerve [n~\ to second abdominal foot. 



Fig. 14. Section through the sixth or last abdominal ganglion passing through the nerves [ra] ; nf, shows 

 the nerve fibres arising from the large ganglion cells and reinforcing the nerves making up the central mass, 

 which is seen to be composed of the union of two separate nervous ends ; X 30 diameters. 



Fig. 15. Transverse section through the middle of the brain, showing the arrangement of the fibres [/a], 

 nucleogenous bodies [nb'] and groups of large ganglion-cells [Igc]. 



Plate VII. 



Fig. 1. Section through upper part of brain of Limulus, passing through the optic nerves [op n]; cm, 

 groups of cells fi-om which the optic nerves appear to arise ; y, Y-shaped bundle of nerve-fibres ; n b, nucle- 

 ogenous bodies on each side of the brain ; I g c, groups of large ganglion-cells ; cm, commissures uniting the 

 brain with the oesophageal ring ; n I, neurilemma. The lettering the same for "all the figures. Magnified 

 15-20 diameters, la, A large ganglion cell of Limulus; 15, the same of the lobster; Ic, small ganglion cells 

 of Limulus ; Id, the same of the lobster ; all magnified 225 diameters to show their relative size and form. 



Fig. 2. Section lower down, just grazing the under side of one optic nerve ; the nucleogenous ruflS^e- 

 shaped bodies in front as well as on the sides ; the Y-shaped bundle of nerves nearly merged with the rest ot 

 the fibrous portion ; the groups of large ganglion-cells [Igc] limited in extent. 



Fig. 3. Section of portion of brain magnified 30 diameters showing the origin of left optic nerve ; f, 

 bundle of nerve-fibres, without cells and nuclei ; n\ a nerve of which an enlarged section is seen at fig. 

 3a, showing the nucleated fibres cut across ; n% a large bundle of nerve-fibres, of part of which, fig. 36, is an 

 enlarged view, showing the nucleated fibres in section, and seen longitudinally with a few nuclei visible ; 

 X 225 diameters ; 3c, a group of large ganglion-cells, with branched nerve-fibres arising from them ; 

 n, nucleus ; nc, nucleolus, magnified 225 diameters ; Sd, a single large ganglion cell, giving origin to a branch- 

 ing nerve. 



Fig. 4. Section of right side of brain passing through the ocellar nerve, o c n; c, commissure with large 

 ganglion-cells and fibres at this point, surrounded by a distinct neurilemma ; ar, artery passing down the 

 back of the brain. Magnified 30 diameters. 



Fig. 5. Section of brain of Limulus through the ocellar nerve [o c n] and the two tegumental nerves 

 [t n] ; c, section of lower part of commissure to oesophageal ring ; Ju ^ the small area on the right side 

 composed of nerve-fibres, showing the asymmetry of the brain ; magnified 30 diameters. 



