534 THE ORIGIN OF VERTEBRATES 



Scaphaspis, 349 

 Schwann, sheath of, 469 

 Sclerotomes, 388 

 Scorpion, hrain, 54 



,, hranchial lamellae, 175 

 ,, development, 482 



,, entochondrites, 377 



„ excretory organs, 397 



eyes, 75 



lung-books, 150, 170 

 ,, lymphatic glands, 423 



,, muscles, oblicme, 278 

 n ,, recti, 271 



., ,, respiration, 171 



,, veno-pericardial, 177 

 ,, muscular system, 247, 268, 269 

 „ nerves to Chelicerse, 237 

 ,, olfactory organs, 220 



„ operculum of male, 189, 206, 212 



pecten, 359, 366, 371, 373, 374, 377 

 ,, under surface, 372 



uterus, 189, 202, 203, 204, 205, 212 

 Sea-scorpions, 25, 26, 27, 56, 150, 170, 191, 208, 221, 232, 235, 241, 349, 359 

 Segmentation, branchiomeric, 124 



body-muscles in vertebrate, 388 

 eye-muscles, 248 



of head, double, 155, 157, 173, 234, 258, 411, 459 

 of head-shield, 339 

 history of cranial, 258 

 Segments, branchial of Ammoccetes, 161, 178, 186 



,, hyoid, in Ammoccetes, double, 186, 201, 267, 300 



,, innervation of branchial, 151 



,, first mesosomatic, in Limulus and its allies, 188 



,, mesosomatic, of Eurypterus, 192 



„ prosomatic of Limulus and its allies, 233, 249 



,, ,, Ammoccetes, 286 



,, of spinal region of Vertebrates, 388 



,, of trigeminal nerve-group, 257, 279 



„ tubular muscles of hyoid, 299 



Sense-organs of Amphioxus, 34 



,, branchial, of Limulus, 359, 360 



,, lateral, of Annelids, 357, 367 



,, lateral-line system, 356, 411, 470 



Serum, 492 



Significance of the optic diverticula, 102 

 Silurus, 488 

 Sinus, longitudinal venous, of Limulus, 176, 312, 451 



,, rhomboidal of bird, 46 

 Skeleton, Ammoccetes, 126, 296, 335 



branchial, 126, 126 

 i, ,, basi-cranial, 132 



» ,, muco-cartilaginous, 291, 296, 330, 331 



