346 XATURAL HISTORY. 



the sarcode of the body and the filaments. Blended portions of the latter, seemingly detached by 

 accident, 'continue to exist as non-nucleated Rhizopodous organisms. 



XLVII. Gromia, discovered by Dujardin in both salt and fresh water, is a round or egg- 

 shaped little mass of granular sarcode, with relatively large central nucleus, vacuoles, contractile 

 vesicle (seen by Wallich), and a tough membranous investment. The last is thin, transparent, and 

 usually open at one end only, whence the sarcode is extruded. This stretches forth in thin branching 

 pseudopods, and also extends itself as a film back over the whole of the test, giving off long delicate 

 pseuclopods from its general surface. These are continually changing in direction and extent, uniting 

 and disuniting among themselves, or moving as lashes, spirals, and otherwise. At their unions they 

 form islets of sarcode, which become the centres of secondary nets. 



A very interesting kind of Gromia (Fig. 13), found by Dr. Leicly among the clamp moss of his 

 house-yard in Philadelphia, is named by him G. terricola. It is about twelve millem. in diameter ; 

 and with its pseudopodial net fully spread, this Gromia looks somewhat like a spider in its web. Its 

 food consists of "minute Diatoms, fragments of Lyngbya, and globular green Algae." It takes in 

 some sand also. 



XL VIII. Many of the Reticularian Rhizopods have a calcareous shell, not a merely spicular or 

 fibrous, basket-like skeleton, like a Radiolarian silicious framework, but composed of definite chambers 

 or compartments, sometimes one, often more, in regular sequence on a straight line, or bent, coiled, 

 alternating, concentric, or even irregularly heaped, in almost endless modifications. These lime-made 

 shells are thus either simple or compound, containing (1) only one round, oval, or elongate morsel of 

 sarcode; or (2) more than one, sometimes very many such little bodies in one shell, which is 

 chambered or divided according to the number of segments of sarcode constituting the whole 

 animalcule. 



On account of this latter condition, these calcareous-shelled Reticularia have been termed 

 Polythalamia.* The first-mentioned, or single-chambered ("nionothalamous") condition, whether 

 regarded as a special form, or as an exception to the general rule, being due either to immature, 

 imperfect, or varietal growth, at all events vitiates the application of " Polythalamia " to the whole 

 of the group. 



The walls separating the chambers of the compound shells are pierced with either one or many 

 holes, for the passage of a thread ("stolonf") or threads of sarcode, by which the segments are 

 connected together, and by which, indeed, each new segment stretches, buds, or grows out from the 

 older portion of sarcode. These simple holes in each separating wall (" septum J") of the chambers 

 in those of the compound shells which look like little Ammonites and Nautiluses were at first 

 thought to constitute a distinction between those high-class Molluscs which have tubes (" siphons " 

 or " siphuncles ") from chamber to chamber, and these minute shells, which were at that time 

 mistakingly referred to that class ; and thus they were called Cephalopoda foraminifera, to distinguish 

 them from the Cephalopoda siphonifera. Although this mistake was soon corrected, the word 

 Foraminifera has been kept for these Reticularian s under notice. 



Some wrongly think that the name is due to the fact that in many instances the whole of the 

 outside shell is perforated with either small holes or minute tubules. In this latter sense, however, 

 the name would not be applicable to the whole of the group ; for in a large and important division 

 the general shell is not pierced with any holes, but has solid walls except at the single aperture 

 whence the sarcode pushes out an external filmy coat and pseudopods, or buds out on a new stolon 

 (Fig. 14). 



Hence Foraminifera are divisible into two main groups : 1. The imperf orate (imperforata), or 

 porcellanous (porcellana) ; 2. The perforate (perforates), or glassy or vitreous (vitrea, also hyalina), 

 on account of their relative translucency. There is also an intermediate group, called the arenaceous, 

 or sandy (arenacea), some of which seem to belong to the one, and some to the other of the fore- 

 going divisions. 



Still there are even in these groups, however distinct they may appear to be at first sight, links 



* Greek, polys, many ; thalamos, bed or chamber. 



t Latin, stolo is used by botanists for a kind of root ; from Greek, stolos, a setting-out or a source. 



% Latin, septum, a hedge or wall. 



