8 14 MICROSCOPIC FORMS OF ANIMAL LIFE 



are of smaller size, and they are so disposed as to present a smooth 

 surface internally, though the exterior is rough. What is most 

 remarkable about this is the geometrical regularity of its form, 

 which is typically triradiate (fig. 615, c), the rays diverging at equal 

 angles from the central cavity, and each being a tube (d) with an 

 orifice at its extremity. Not unfrequently, however, it is quadri- 

 radiate, the rays diverging at light angles ; and occasionally a fifth 

 ray presents itself, its radiation, however, being generally in a 

 different plane. The three rays are normally of equal length; but 

 one of them is sometimes shorter than the other two ; and when 

 this is the case the angle between the long rays increases at the 

 expense of the other two, so that the long rays lie more nearly in a 

 straight line. Sometimes the place of the third ray is indicated 

 only by a little knob ; and then the two long rays have very nearly 

 the same direction. We are thus led to forms in which there is no 

 vestige of a third ray, but merely a single straight tube, with an 

 orifice at each end ; and the length of this, which often exceeds 

 half an inch, taken in connection with the abundance in which it 

 presents itself in dredgiiigs in which the triradiate forms are rare, 

 seems to preclude the idea that these long single rods are broken 

 rays of the latter. It is undoubtedly in this group that we are to 

 place the genus Hcdiphysema, which, from constructing its 'test' 

 entirely of sponge-spicules, and even including these in its pseudo- 

 podial expansions, has been ranked as a sponge, although observation 

 of it in its living state leaves no doubt whatever of its rhizopodal 

 character. 1 



Lituolida. The type of this family, which is named after it, is 

 a large sandy many-chambered fossil form occurring in the chalk, 

 to which the name Lituola was given by Lamarck, from its resem- 

 blance in shape to a crosier. A great variety of recent forms, mostly 

 obtained by deep-sea dredging, are now included in it, as bearing 

 a more or less close resemblance to it and to each other in their 

 chambered structure, and in the arrangement of the sand-grains of 

 which their tests are formed. These grains are, for the most part. 

 finer than those of which the tests of the preceding family are con- 

 structed, and are set (so to speak) more artistically, and a con- 

 siderable quantity of a cement exuded by the animal is employed 

 in uniting them. This is often mixed up with sandy particles of 

 extreme fineness to form a sort of ' plaster ' with which the exterior 

 of the test is smoothed off, so as to present quite a polished surface. 

 It is remarkable that the cement contains a considerable quantity 

 of oxide of iron, which imparts a ferruginous hue to the ' tests ' in 

 which it is largely employed. The forms of the Litiinllne ' tests ' 

 often simulate in a very curious way those of the simpler types of 

 t he vitreous series. Thus, the long spirally coiled undivided sandy 

 tube of Ammodiscus is the isomorph rf S}>irtUina. In the genus Haplo- 

 phragmium (fig. ()]4.n./>. and Plate XVIII, fig. C>) we have singular 

 imitations of t he < ilobigerine. Rotaline, and Nonionine types ; and in 



1 See Mr. Seville Kent in Aim. <>f ^,t. ll/\f. ser. v. vol. ii. 1878; Professor Ray 

 in (Jtnti-t. Jonni. Micninr. ,sv/'. vol. xix. 1878, p. 17C> ; and Prof essor Mobius's 



ii run Mti /tri/i/ix, 



