494 THE PINEAL ORGAN 



Romberg's sign : if the patient closes his eyes when standing with the feet 

 together, he sways from side to side, and if not supported will eventually 

 fall. It occurs in cases, such as locomotor ataxia, in which there is a 

 loss of the deep reflexes, which are concerned in maintaining the erect 

 posture. 

 Salpa (L. salpa, stock-fish) : a tunicate belonging to the order Thaliacea. A 

 median horseshoe-shaped eye is present, and sometimes small accessory 

 eyes. 

 Sauria (Gr. saura, lizard) : term applied to lizard-like reptiles in general, but 



sometimes restricted to the crocodiles and Lacertilia. 

 Sauropsida (Gr. saura, lizard ; opsis, appearance) : the name given collectively 



to the two classes Birds and Reptiles. 

 Schizochroal eyes (Gr. schizo, cleave, separate ; chroa, surface) : the term 

 applied to the type of lateral compound eye of trilobites in which the 

 constituent units of the eye were separate, the areas between the corneal 

 facets being occupied by an interstitial test or sclera. 

 Sepia (L. sepia, cuttle-fish) : a mollusc belonging to the class Cephalopoda 

 possessing ten arms or feet and highly developed eyes. The name 

 " sepia " is also used for the black pigment which is obtained from it. 

 Stemma (Gr. stemma, crown or wreath) : the simple eyes or ocelli of certain 



invertebrates, e.g. the frontal stemmata of insects. 

 Tapetum (Gr. tape, L. tapetum, carpet, many-coloured garment or tapestry) : 

 T. argentea, the silvery or greenish-gold, iridescent membrane between 

 the lamina fusca and choroid coat in certain Teleost fishes. The irides- 

 cence is due to crystals of calcium salts deposited in the cells : syn. 

 T. cellulosum. T. pellucidum, a delicate fibrous membrane in the choroid 

 coat next the retina. It has a metallic lustre due to the reflection and 

 interference of light rays by the fibrillar in the membrane. It is found 

 in certain fishes, carnivores, and ungulates, e.g. the horse and ox. Reflect- 

 ing membranes behind or external to the retina are also found in some 

 invertebrate eyes and luminous organs, e.g. the photospheria, found on 

 the first abdominal segments of Nyctiphanes. 

 Tetrabranchiata (Gr. tetra, four ; branchia, gills) : a subclass of the Cephalo- 

 poda, having four comb-like gills or ctenidia. It includes one living 

 genus, Nautilus, and the extinct Ammonites are usually referred 

 to it. 

 Tretaspis (Gr. tretos, perforated ; aspis, shield) : the name given to the larval 

 form of a genus of the trilobites characterized by " holes " or eye-spots 

 on the glabellum. 

 Triassic System or Period : the lowest strata of the Mesozoic period, during 

 which mammal-like reptiles first made their appearance. It comprised 

 the Rhoetic, Keuper, and Bunter series. 

 Trilobita (Gr. treis, three ; lobes, lobe) : an extinct Order of crustaceans. 

 The dorsal aspect is divided into three lobes, a median or axial and 

 lateral or pleural. In many the labrum or hypostome supports a pair 

 of compound eyes ; and a median eye-tubercle is present in the larval 

 fossils of certain forms, e.g. Trinucleus. 



