80 



THE MICROSCOPE AND ITS KEVELATIONS. 



ules laid side by side with extraordinary regularity. The genus Rhab- 

 dammina (Sars) resembles Saccamina in the structure of its ' test,' which 

 is composed of sand-grains very firmly cemented together; but the grains 

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

 face internally, though the exterior is rough. What is most remark- 

 able about this, is the geometrical regularity of its form, which is typically 

 triradiate (Fig. 321, c), the rays diverging at equal angles from the 

 central cavity, and each being a tube (cl) with an orifice at its extremity. 

 Not unfrequently, however, it is quadri-radiate, the rays diverging at 

 right angles; and occasionally a fifth ray presents itself, its radiation, 

 however, being on 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 litttle 

 knob: and then the two long rays have very nearly the same direction. 



FIG. 320. 



Arenaceous Foraminifera: a, 6, upper and lower aspects of Halophragmium globigerini forme; 

 c, Hormosina globulifern; d, Marsipella elongata; e, terminal portion, and /, middle portion of 

 the same, enlarged; g, Thurammina papillata; h, portion of its inner surface enlarged. 



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 dredgings 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 Halipliysema; which, from constructing its ' test ' en- 

 tirely of sponge-spicules, and even including these in its pseudopodial ex- 

 pansions, has been ranked as a Sponge, although observation of it in its 

 living state leaves no doubt whatever of its Khizopodal character. 1 



1 See Saville Kent in "Ann. of Nat. Hist.," Ser. 5, Vol. ii. (1878); Prof. R. 

 Lankester in "Quart. Journ. Microsc. Sci.," Vol. xix. (1868), p. 476; and Prof. 

 Mobius's " Foraminifera von Mauritius." 



