GENUS ORBULINA. 177 



shell. In the OrhulincE of comparatively shallow waters, the shell seems to retain through life 

 its hyaline aspect, not appearing to receive any augmentation in thickness subsequently to its 

 first formation. In those brought up from deeper waters, on the other hand, we commonly 

 find the original hyaline shell to be encrusted by an exogenous deposit of coarser texture and 

 of a reddish hue, having a peculiar sculptured surface (fig. 8, a) which reminds the observer 

 of that of some of the hispid pollen-grains. 



280. Not unfrequently this exogenous deposit, instead of closely adhering to the surface 

 of the shell which it encloses, forms a distinct sphere that is exactly fitted to it without being 

 continuous with it, — a circumstance which seems first to have been pointed out by Mr. 

 Pourtales,* who supposed that the inner shell is the more recent or younger, and that the outer 

 one is the older and is destined to be cast off. Of this, however, I see no evidence whatever; 

 whilst, on the other hand, not only is it found that a more delicate hyaline layer always 

 exists within the outer less transparent coat (as may be easily shown by removing the latter by 

 the careful application of dilute acid), but this outer layer is occasionally so loosely applied to 

 the interior, that a considerable space remains between them over a larger or smaller portion 

 of the surface of the sphere, so that the outer layer forms a protuberance enclosing an 

 additional chamber, which is sometimes of small proportionate size, but sometimes has nearly 

 the dimensions of the original sphere. (This seems to be the form described by D'Orbigny, 

 Lxxiii, as Globif/erina bilobnta.) In one specimen in my possession, the sphere bears two such 

 protuberances, both of them small. It is particularly worthy of note that the secondary cavity 

 thus formed has no other communication with the single cavity of the original sphere, than 

 that which is afforded by the ordinary pores of the shell-wall ; there being no apertural 

 passage between the two. Hence, although such an excrescence may in some sense be 

 regarded as a sort of attempt at the formation of a new chamber, the rarity of its presence 

 seems to forbid the idea that its formation is anything but abnormal. In fact the perfection 

 of the spherical form in all but such extraordinary specimens of OrbuUna is extremely 

 remarkable ; there being not the slightest indication on any part of their surface of ever 

 having been attached by adhesion to any other organism, still less of ever having been con- 

 tinuous with any other fabric and having been separated from it by fracture. 



281. It is affirmed, however, by Mr. Pourtales (loc cit.), that in nearly one half of the 

 Orbulina which he examined among the large number of well-preserved specimens obtained 

 from the bottom beneath the Gulf Stream by the U.S. Coast Survey, he found "young 

 Globigerinm more or less developed, and attached to the inside of the OrbuUna by numerous 

 very slender spicules. Only one Globigerina is developed in an Orhulina, whose cavity it 

 gradually fills up, and whose shell it finally bursts to make its escape. At that time the 

 Globigerina has already nearly attained its full size ; and I have counted as many as sixteen 

 cells in a specimen having yet room for several more before filUng up the parent Orbuhna." 

 It is not rare, continues the same observer, to find Orbulince with the double shells just 

 described containing young Globigerina. Further, it is stated by Prof. Schultze (xcix), that 

 Dr. August Krohn has seen exactly the same thing in living Orbulince captured with the 



* 'Silliman's Journal,' July, 1858, p. 96; and 'Annals of Natural History,' September, 

 1858, p. 236. 



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