FORAMINIFERA AND BADIOLAKIA. 69 



minifera; one of the most frequent forms of it being a regular alterna- 

 tion of ridges and furrows, such as is occasionally seen in Miliola (Plate 

 xv., fig. 3), but which is an almost constant characteristic of Peneroplis 

 (fig. 5). But no difference of texture accompanies either this or any 

 other kind of inequality of surface; the raised and depressed portions 

 being alike homogeneous. In the shells of the vitreous or hyaline type, 

 on the other hand, the proper shell- substance has an almost glassy trans- 

 parence, which is shown by it alike in thin natural lamellae, and in arti- 

 ficially prepared specimens of such as are thicker and older. It is 

 usually colorless, even when (as in the case with many Rotalince) the 

 substance of the animal is deeply colored; but in certain aberrant Rota- 

 lines the shell is commonly, like the animal body, of a rich crimson hue. 

 All the shells of this type are beset more or less closely with tubular perfo- 

 rations, which pass directly, and (in general) without any subdivision, 

 from one surface to the other. These tubuli are in some instances suffi- 

 ciently coarse for their orifices to be distinguished with a low magnifying 

 power, as i punctations ' on the surface of the shell, as is shown in Fig. 

 314; whilst in other cases they are so minute as only to be discernible in 

 thin sections seen by transmitted light under a higher magnifying power, 

 as is shown in Figs." 335, 336. When they are very numerous and closely 

 set, the shell derives from their presence that kind of opacity which is 

 characteristic of all minutely-tubular textures, whose tubuli are occupied 

 either by air or by any substance having a refractive power different from 

 that of the inter tubular substance, however perfect may be the transpar- 

 ence of the latter. The straightness, parallelism, and isolation of these 

 tubuli are well seen in vertical sections of the thick shells of the largest 

 examples of the group, such as Nummulina (Fig. 335). It often hap- 

 pens, however, that certain parts of the shell are left unchannelled by 

 these tubuli; and such are readily distinguished, even under a low mag- 

 nifying power, by the readiness with which they allow transmitted light 

 to pass through them, and by the peculiar vitreous lustre they exhibit 

 when light is thrown obliquely on their surface. In shells formed upon 

 this type, we frequently find that the surface presents either bands or 

 spots which are so distinguished; the non-tubular bands usually marking 

 the position of the septa, and being sometimes raised into ridges, though 

 in other instances they are either level or somewhat depressed; whilst the 

 non-tubular spots may occur on any part of the surface, and are most 

 commonly raised into tubercles, which sometimes attain a size and num- 

 ber that give a very distinctive aspect to the shells that bear them. 



460. Between the comparatively coarse perforations which are com- 

 mon in the Rotaline type, and the minute tubuli which are characteris- 

 tic of the Nummuline, there is such a continuous gradation as indicates 

 that their mode of formation, and probably their uses, are essentially the 

 same. In the former, it has been demonstrated by actual observation 

 that they allow the passage of pseudopodial extensions of the sarcode- 

 body through every part of the external wall of the chambers occupied 

 by it (Fig. 314); and there is nothing to oppose the idea that they 

 answer the same purpose in the latter, since, minute as they are, their 

 diameter is not too small to enable them to be traversed by the finest of 

 the threads into which the branching pseudopodia of Foraminifera are 

 known to subdivide themselves. Moreover, the close approximation of 

 the tubuli in the most finely-perforated Nummulines, makes their col- 

 lective area fully equal to that of the larger but more scattered pores of 

 the most coarsely-perforated Rotalines. Hence it is obvious that the 



