50 



n a. Ocellar nerve. w 11. 7th Epimeral uerve. 



tiA. Ocular nerve. n 12. 8th Epimeral nerve. 



n 3. Gastric nerve. » 13. 9th Epimeral nerve. 



w,4. 1st Epimeral nerve. « 14. 10th Epimeral nerve. 



n 5. 2nd Epimeral nerve. n 15. 11th Epimeral nerve. 



n 6. Its recvirrent branch. n 16. 12th Epimeral aerve. 



n 7. 3rd Epimeral nerve. « 17. ] 3th Epimeral nerve. 



n 8. 4th Epimeral nerve. n 18. 14th Epimeral nerve. 



n 9. 5th Epimeral nerve. « 19. 15th Epimeral nerve. 



n 10. 6th Epimeral nerve. ' ' pi- Pleonal plexus. 



(The preparation is No. 1303 c, in the Physiological Series of the Museum of the Royal College 

 of Surgeons.) 

 Fig. 2. Left gill-limb, with attached branchia. 

 a. Tract of efferent branchial vessels. 

 Fig. 3. Branchial lamella ; a, efferent plexus. 



All the figures, save where otherwise stated, are of tlie natural size. 



Woodcuts. 



Fig. 1. Cell-egg, with yolk-cells developing: magnified 130 diameters [Lhnulus polyjihemus). 

 Fig. 2. Impregnated egg after disappearance of primitive cells ; magnified 30 diameters : id. 

 Fig. 3. Section of egg-coat and germ-trace : magnified 130 diameters : id. 

 Fig. 4. Ovum with embryo-trace : magnified 10 diameters : id. 



Fig. 5. Ovum with embryo further developed, side view: magnified 10 diameters: id. 

 Fig. 6. Ovum with embryo, under-view : magnified 10 diameters : id. 

 Fig. 7. Embryo Lhnulus, just before hatching, back view : magnified 13 diameters. 

 Fig. 8. Newly hatched Lhnulus, under-view : magnified 9 diameters. 

 Fig. 9. Nauplius, or young of Apus cancriformis : magnified. 

 Fig. 10. Nmiplius, or young of Cyclops quadricornis : magnified. 

 Fig. 11. Zoea, or larva of Penceus. 

 Fig. 12. Five stages of the development of a Trilobite [Trinucleus ornatus, Stb.), selected from the more ft 



numerous series in Barrande's ' Systeme Silurien du Centre de la Boheme,' 4to, 1852, pi. 30. , 



a. Larva consisting of the cephaletron a, and pleon c : b. Larva showing the characteristic elon- 

 gation of the posterior angles of the cephaletron, or " genal spines : " c. Larva with one thorac- 

 etral segment b : d. Larva with two thoracetral segments b; e. Young animal showing mature 

 number of six thoracetral segments b, and fully lengthened " genal spines." 

 Fig. 13. Eimjpterus Scouleri, Hbt. ; reduced restoration (Carboniferous Limestone). 

 Fig. 14. Pterygotus anglicus, Ag. ; reduced restoration (Devonian of Forfarshire) . 

 Fig. 15. Slimonia acuminata, H. Wd. ; reduced restoration (Upper Silurian). 

 Fig. 16. Styloneurus Logani, H. Wd. ; reduced restoration (Upper Silurian). 

 Fig. 17. Prestwichia rotundata, H. Wd. ; two-thirds nat. size (Coal-measures). 

 Fig. 18. Hemiaspis limuloides, H. Wd. ; two- thirds nat. size (Lower Ludlow). 



(The figures 12-18 are copied from those reproduced by H. Woodward, in his excellent paper 

 " On the relationship of the Xiphosura to the Eurypterida and to the Trilobita and Arach- 

 nirla" in the 'Popular Science Review' for October 1872.) 



