44 OF THE FORAMINIFERA GENERALLY : 



animal from the polypary, when each type of skeleton has been examined in connection with 

 the soft body it supports. On the other hand, we not unfrequently find that a close resem- 

 blance in the structure of the polypary masks an essential diversity in the organization of the 

 animal ; certain horny skeletons of H^/drosoa being scarcely distinguishable from those of 

 Poli/zoa, although the former belong to true Zoophytes, whilst the latter are members of the 

 Molluscous sub-kingdom. 



56. It seems obvious, then, that no classification of Foraminifera can be thoroughly 

 satisfactory, which is based rather on the characters of their shells than on those of the 

 animals by wliich those shells are formed ; and it is unfortunate tliat our knowledge of the 

 latter is as yet so imperfect, as to afford us but a ver}^ slight foundation for a natural arrange- 

 ment of the group. It may be questioned, indeed, whether the extreme indijferenHsm of 

 structure which seems to be a general characteristic of the Rhizopod type and to reach its 

 acme in the Foraminifera, will not always prevent the systematist from finding the study of 

 the animal of much avail to him ; and whether he will ever be relieved from the necessity of 

 placing his chief reliance on those features in the structure of the shell, which may be 

 regarded as most surely indicating the potentialities of the apparently homogeneous jelly-like 

 mass which it encloses. Such, at any rate, must be his method of procedure under existing 

 circumstances ; and as there is at present nothing to be added to the general account alread}' 

 given of the structure and life-history of the sarcode-bodies of the Foraminifera, our attention 

 will be now directed to the characters furnished by the investments which they form, with a 

 view to determine what are those on which the primary and secondary subdivisions of the 

 group may be most satisfactorily based. 



57. Texture of the Skell. — In the shells of Foraminifera, as was correctly pointed out by 

 Prof. Williamson (ex, p. xi), three very distinct varieties of texture are easily recognisable : 

 the porcellanous, Xhe hyaline or vitreous, and the arenaceous. — In the first of these varieties the 

 shell, when viewed by reflected light, presents an opaque-white aspect, which bears a strong 

 resemblance to that of porcelain, especially when (as in Penerojjiis) its surface is highly 

 polished. When thin natural or artificial laminae of it, however, are viewed with transmitted 

 light, the opacity gives place to a rich brown or amber -colour, which seems to be imparted 

 by the animal matter that is united with the calcifying deposit, the colour of the sarcode-body 

 being usually the same as that of the shell. In a few instances both the shell and the animal 

 body have a rich crimson hue. No structure of any kind can be detected in this kind of 

 shell-substance, which is apparently homogeneous throughout. When shells of this character 

 are decalcified by dilute acid, a delicate, gelatinous-looking substratum of animal matter is 

 left, very distinct in its aspect from the sarcode-body which the shell included (Plate IV, fig. 14). 

 This, in fact, seems to bear the same relation to the protoplasmic substance, that the cellulose 

 wall of the vegetable cell bears to the " endoplast" from the surface of which it is excreted ; 

 and just as in Biatomacece the consolidation of that exudation by silex forms the beautiful lorica 

 characteristic of that group, so here does the consolidation of an analogous excretion-layer by 



alcareous deposit form the shellv wall of each segment of the animal. Although the shells 

 of the porcellanous type often present the aooearance of bemg perforated with foramina, yet 

 this appearance is illusory, being due to a mere " pitting" of the external surface, which pitting 



