268 THE GALAPAGOS TORTOISES. 



season, there may be a thick and strong covering that is increased in thickness 

 by successive growths in its duration. The earUest slough in some marine 

 tortoises is well described in Fry's remarks on Chelonia depressa in, 1913, 

 Records of the AustraHan Museum, 10, p. 162, "Chelonia depressa then, emerges 

 from the egg with each scute covered by a ' larval shield ' which, as the animal 

 grows, becomes an areola almost identical with that found in land tortoises; 

 this is finally shed before the turtle reaches maturity, leaving the smooth scutes 

 described by Garman and figured on PI. XXI-XXII. As far as I can ascer- 

 tain these areolae are unique amongst Marine turtles." Giinther, 1877, dis- 

 cussing the land tortoises of the Galapagos, says, p. 18, as long as the Tortoises 

 are young, growth, as far as it is externally visible, proceeds along the margins 

 of all the scutes; the sutures get broader, appearing as whitish seams, soft and 

 very sensitive. After some time the young portion of the epidermis becomes 

 horny, and is raised in a line (stria) running along each side of the suture. At a 

 later period this increment takes place only (at least only conspicuously) in 

 certain portions of the carapace." Marine and all land tortoises are hatched 

 with the larval shield on each scute; it forms the areolar space on the scute 

 which in the land species may or may not be shed, but which appears to be 

 shed in marine forms at an early date. If not shed all the concentric striae 

 remain, unless possibly affected by wear, each successive stria being the index 

 to the amount of surface enlargement or growth, beyond the stria immediately 

 preceding it. If there were no lateral growth, from starvation or disease, the 

 scute, if there were no slough, might thicken by successive accretions beneath 

 but possibly might not increase the number of concentric striae around its 

 edges. Some specimens from dry localities, have retained the larval shield 

 and have never sloughed; year after year they have increased by one or more 

 the record of the striae on the scute. Other specimens appear to have kept 

 the sloughs and striae for long periods then suddenly by a slough have lost 

 the entire record of the series at once and from the striate and grooved condi- 

 tion have become smooth and poHshed, to begin at the edges of each scute 

 another striated record, see Plate 27. Testudo clivosa, Plate 21, a twenty-five 

 inch specimen may have an entire record. On the youngest specimens, a year 

 or more of age, of most if not all of the species in the collection, no slough has 

 occurred. The larval shield and all of the striae are in place. Larger speci- 

 mens of some of the same species show plainly that through a slough the larval 

 shield and the striae have been carried away leaving the carapace smooth; 

 still larger ones testify to more or less regularity in sloughing and to consequent 



