FORAMIN1FERA AND BADIOLARIA. 



87 



exudes through the pores of the shell, forming a flocculent fringe around 

 it; and this extends itself on each of the spines, creeping up one side to 

 its extremity, and passing down the other, with the peculiar flowing 

 movement already described ( 395). The whole of this sarcodic ex- 

 tension is at once retracted if the cell which holds the Globigerina receives 

 a sudden shock, or a drop of any irritating fluid is added to the water it 

 contains. It is maintained by Sir Wyville Thomson that the bottom-de- 

 posit is formed by the continual ' raining-down ' of the Globigerinae of 

 the upper waters, which (he affirms) only live at or near the surface, and 

 which, when they die, lose their spines and subside. But it has been 

 shown by the careful comparison made by Mr. H. B. Brady between the 

 surface-gatherings and the bottom-deposits of the same areas, that the 

 two> are often so marked, as to forbid the idea that the latter are solely 

 derived from the former. 1 For not only are there several specific types 



Fig. 326. 



upon original uharnber-wall, which is raised into ridges with tubuli between them, and includes 



found in each, which do not present themselves in the other, but, as a 

 rule, the shells of the types common to both are larger and thicker in 

 the latter than they are in the former. This evidence strongly supports 

 the conclusion originally drawn by the Author from his own examination 

 of the Globigerina-ooze, that the shells forming its surface-layer must 

 live on the bottom, being incapable of floating in consequence of their 

 weight; and that if they have passed the earlier part of their lives in the 

 upper waters, they drop down as soon as the calcareous deposit continu- 

 ally exuding from the body of each animal, instead of being employed in 

 the formation of new chambers, is applied to the thickening of those 



1 " Quart. Journ. Microsc. Sci., " Vol. xix. (1879), p. 295. 



