TEMORA. 



[ 635 ] 



TEST-OBJECTS. 



further formation of new cells and fresh 

 deposition, the structure of the teeth becomes 

 more and more consolidated, the spongy 

 tissue of the enamel gradually being ab- 

 sorbed. 



When the entire enamel and a consider- 

 able portion of the ivor}' have been formed 

 in the capsules, these become too small to 

 contain the teeth, which then rupture them, 

 and continue to grow at the root, until the 

 crown projects above the margin of the jaw. 

 The remainder of the capsule then forms 

 the periosteum of the alveoli, and by depo- 

 sition from the side next the tooth, produces 

 the cement. 



The permanent teeth are formed upon the 

 same plan ; — the three last molars in the 

 remains of the j^rimitive dental groove ; the 

 others in distinct sacs, called reserve sacs, 

 and formed in the wall of the follicles of 

 the milk-teeth. 



The teeth of animals present numerous 

 interesting varieties, to which we can but 

 briefly refer. Thus in the Mammalia, the 

 enamel is often absent; the cement fre- 

 quently extends over the croT^'n ; the three 

 component structures are folded ; the teeth 

 are compound; the ivory contains Haversian 

 canals, and the ivorv-tubes enter the enamel. 

 In reptiles the teeth are often anchylosed to 

 the jaws. In fishes the teeth are often 

 solid ; the ivor}^ is furnished with Haversian 

 canals, sometimes isolated, and each sur- 

 rounded by a layer of ivory and cement, so 

 that the teeth appear to consist of aggrega- 

 tions of little teeth; the vessels often 

 branch and anastomose freely ; the ivory 

 tubes are often ver}* large or absent, the ivory 

 then consisting of a finely granular base with 

 numerous vascular canals, true enamel ap- 

 pearing to be absent. 



The method of making sections of teeth is 

 described under Preparation. They 

 should be very thin and preserved in the dry 

 state. 



BiBL. Kolliker, M'lkroskop. Anat. ii. 54; 

 OwenjOdontograjjhy, and Todd's Cycl. Anat. 

 ^•c, iv. 864; Goodsir, Edinh. Med. and 

 Surg. Journ. 1839. i. ; Tomes, Lectures on 

 Dental Surgery, 8fc., and Phil. Trans. 1849, 

 1850; Nasmyth, Researches on the Teeth; 

 Retzius, MuUer's Archiv, 1837. 486 ; 

 Heusinger, Histologic. 



TEMORA, Baird.— A genus of Entomo- 

 straca, of the order Copepoda, and family 

 Diaptomidse. 



Char. Thorax composed of five, abdomen 

 of three joints; lesser antenna? two-branched; 



first four pairs of legs each giving ofi^ a two- 

 jointed branch. 



T. finmarchica. Found on the coast of 

 Ireland. 



BiBL. Baird, Brit. Entomostr. 227. 



TENDON. See Ligaments. 



TENTHREDO, Leach.— A genus of Hy- 

 menopterous Insects, of the order Tenthi'e- 

 dinidae (Saw-flies). 



The species of Tenthredo and of the other 

 genera belonging to the family, both of 

 which are very numerous, are interesting on 

 account of the remarkable structure of the 

 ovipositor, which consists of two flattened 

 and curved saw-like plates. These are used 

 to saw the leaves of plants, for the deposi- 

 tion of the eggs. 



The insects are found upon gooseberrj^- 

 bushes, rose-bushes, the white thorn, the 

 willow, alder, poplar, the plum and other 

 fruit-trees, cabbage, turnip, bramble, &c. 

 The larvae are very destructive to agricul- 

 tural crops. 



T. nassata is represented in fig. 367 (p. 362) . 



BiBL. Westwood, Introduction, c^c. ii. 90, 

 and the Bihl. therein. 



TERPSINOE, Ehr.— A genus of Diato- 

 maceae. 



Char, Frustules tabular, obsoletely stipitate, 

 subsequently connected by isthmi, and with 

 transverse, short, interrupted, capitate vittse; 

 valves in side view with lateral inflations. 



T. musica (PL 14. fig. 33, side view; PI. 

 19. fig. 10, front \dew). Frustules very faintly 

 punctate, in front view rectangular oblong ; 

 side view equally inflated in the middle and 

 at the ends, in older specimens constricted 

 in the middle, inflated beyond the middle 

 towards both ends, the apices produced and 

 obtuse, the nodules separated by septa. 

 Length 1-180". 



T. indica {Anaulus ind., E.). 



BiBL. 'Ehrenherg, Abhand. d. Berl. Akod. 

 1841. 402; Kiitzing, Bacill. 128, Sp. Alg. 

 119. 



TESSELLA, Ehr.— A genus of Diato- 

 macese. 



Char. Frustules broadly tabular, not con- 

 catenate, with crowded, longitudinal, alter- 

 nate vittae, interrupted in the middle ; stipes 

 absent (?). Marine. 



T. interrupta (PL 14. fig. 35). Length of 

 frustules 1-580; breadth 1-560 to 1-120". 

 Found with Striatella. 



BiBL. Ehrenberg, Infus. 202 ; Kiitzing, 

 Bacill. 125, Sp. Alg. 114. 



TEST-BOX. Introduction, p. xxiii. 



TEST-OBJECTS.— Test objects are mi- 



