182 FAMILY GLOBIGERINIDA. 



trical plan of growth, so as to give them somewhat of a nautiloid aspect, their essentially 

 globigerine character, however, being still marked by the distinctness of the apertures of the 

 several segments : and other forms are flat, with raised edges and elevated septal bands. 



294. The newly formed segments of Ghhigerina have their chamber-walls composed of 

 a hyaline shell-substance, which is perforated by minute tubuli of uniform size arranged at 

 pretty regular distances. The diameter of these tubuli varies in different specimens from 

 about l-10,000th to l-5000th of an inch; but we nowhere meet with any pores at all 

 approaching in size to the large pores of Orbulina, nor do we find pores of two very different 

 dimensions coexisting in the same individual. In the Globigerina of shallow waters, the walls 

 of the chambers retain through life their original thinness and transparence ; but in those 

 of deeper seas they are generally thickened by exogenous deposit, the surface of which is 

 raised sometimes into minute tubercles, and sometimes into ridges, in the depressions between 

 which are seen the orifices of the pores ; and specimens are frequently met with, in which 

 the ridges form a regular reticulation, with the opening of one of the pores in each areola. 

 Sometimes the ridges bear acicular prolongations ; as is well seen in some of the symmetrical 

 specimens that abound in the Red Sea, in which the needles are so long as to subdivide the 

 large arched aperture of the later chambers. In other instances, again, the entire ridge 

 surrounding each areola rises so high from the surface, as actually to form a tube that 

 encloses the pseudopodium in its course outwards from the pore of the chamber-wall ; this 

 peculiar condition has been observed in nautiloid (symmetrical) specimens from 1600 or 1700 

 fathoms' depth between Malta and Crete and from the deeper parts of the Red Sea. 



295. Each chamber is occupied during life by a reddish-yellow segment of sarcode, 

 from which pseudopodia are seen to protrude ; and it seems probable that the sarcode-body 

 also fills the umbilical vestibule, since without some such connecting band it is difficult to 

 understand how the segments which occupy the separate chambers can communicate 

 directly with each other, or how new segments can be budded off. It has been noticed by 

 Dr. Wallich (civ a) that in the Ghligerino: brought up from great depths the hue of the 

 sarcode-body is dingy, and inclines rather to brown than to yellow ; whilst its particles are 

 less united into a viscid mass, and more disinclined to coalesce again after being crushed 

 asunder, than they are in the specimens obtained from shallower waters. Moreover, he has 

 in no instance seen the pseudopodia extended in deep-sea specimens ; but their surface, 

 when they are newly taken out of the water, is studded with little yellow-coloured masses, 

 closely applied to, and somewhat larger than, the apertures from which they emerge ; and 

 these masses are not unfrequently visible even on the surface of the dry shell! 



296. Affinities. — This genus stands alone among the polythalamous Foraminifera of the 

 hyaline series, in having its shell composed of an aggregation of segments which are merely 

 connected by external adhesion, and have no internal communication w-ith each other. In 

 this respect it corresponds with Ladylopora and Acicularia among the porcellanous forms ; 

 bearing, like them, a really stronger resemblance to its monothalamous than to its polythala- 

 mous congeners (^ 203). If the new segments of Orbulina, instead of detachmg themselves 

 (as they ordinarily seem to do) previously to the formation of their investing shell, were to 



