82 THE MICROSCOPE AND ITS REVELATIONS. 



the ordinary nodosarine type, their tests being sometimes constructed 

 with the regularity characteristic of the shells of the true Nodosaria 

 (Plate xv., fig. 10); whilst in other cases the chambers are less regularly 

 disposed (Fig. 321, /), having rather the character of bead-like enlarge- 

 ments of a tube, whilst their walls show a less exact selection of material, 

 sponge-spicules being worked-in with the sand-grains, so as to give them 

 a hirsute aspect. A greater rudeness of structure shows itself in the 

 nodosarine forms of the genus Reopliax; in which not only are the sand- 

 grains of the test very coarse, but small Foraminifera are often worked- 

 up with them (Fig. 321, e). A straight, many-chambered form of the 

 same genus (Fig. 321, , b) is remarkable for the peculiar finish of the 

 neck of each segment; for whilst the test generally is composed of sand- 

 grains as loosely aggregated as those of which the test of Astrorhiza is 

 made up, the grains that form the neck are firmly united by ferruginous 

 cement, forming a very smooth wall to the tubular orifice. 



FIG. 322. 



Cyclammina cancellata: showing at a, its external aspect; 6, its internal structure; c, a por- 

 tion of its outer wall more highly magnified, showing the sand-grains of which ic is built up, and 

 the passages excavated in its substance. 



476. The highest development of the ' Arenaceous ' type at the pres- 

 ent time is found in the forms that imitate the very regular nautiloid 

 shells, both of the 'porcellaneous' and the 'vitreous' series; and the 

 most remarkable of these is the Cyclammina cancellata (Fig. 322), which 

 has been brought up in considerable abundance from depths ranging 

 downwards to 1,900 fathoms, the largest examples being found within 

 700 fathoms. The test (Fig. 322, a) is composed of aggregated sand- 

 grains firmly cemented together and smoothed over externally with 

 'plaster,' in which large glistening sand-grains are sometimes set at regu- 

 lar intervals, as if for ornament. On laying open the spire, it is found to 

 be very regularly divided into chambers by partitions formed of cemented 

 sand-grains (); a communication between those chambers being left by 

 a fissure at the inner margin of the spire, as in Operculina (Plate xvi., 

 fig. 2). One of the most curious features in the structure of this type, 

 is the extension of the cavity of each chamber into passages excavated in 

 its thick external wall; each passage being surrounded by a very regular 

 arrangement of sand-grains, as shown at c. It not unfrequently happens 



