GLOBIGERINA 



821 



of the ocean by the ' tow net,' which was systematically carried on 

 during the voyage of the ' Challenger,' brought into prominence the 

 fact that these waters in all but the coldest seas are inhabited by 

 floating Glvlnyeruice, whose shells are beset with multitudes of de- 

 licate calcareous spines, which extend themselves radially from the 

 angles at which the ridges meet to a length equal to four or five 

 times the diameter of the shell (fig. 621). Among the bases of these 

 spines the sarcodic substance of the body exudes through the pores 

 of the shell, forming a flocculent fringe around it ; and this extends 



FIG. 620. Globigt-rina conglobuta (Brady): , b, c, bottom specimens ; 



(7, section of shell. 



itself 011 each of the spines, creeping up one side to its extremity, 

 ;md passing down the other with the peculiar flowing movement 

 already described. The whole of this sarcodic extension is at once 

 retracted if the cell which holds the Globigerina receives a sudden 

 shock, or a drop of any irritating fluid is ;nlded to the water it con- 

 tains. It was maintained by Sir "Wyville Thomson that the bottom 

 deposit is formed by the continual ' raining down ' of the GlobigeriB.se 

 of the upper waters. Avhich (he affirmed) only live at or near the sur- 

 face, and which, when they die, lose their spines and subside. The 



