256 REPORT OF NATIONAL MUSEUM, 1897. 



each chamber has a complete wall of its own, thus making double par- 

 titions between them. In some of these higher types there is devel- 

 oijed also what is called a "supplemental skeleton," which consists of 

 a deposit of shell-substance on the outside of the original wall, thereby 

 adding to its thickness, filling in the hollows between the segments and 

 at the umbilici, and sometimes growing out into protuberances of 

 various shapes. This supplemental skeleton is generally traversed by 

 a set of canals or sinuses — passages left during the deposit of the 

 shell-substance, and probably occupied by threads of sarcode during 

 the life of the animal. 



The separation into families, genera, and species of a group of ani- 

 mals like the foraminifera, where variation is the rule and passage from 

 one type to another is by a sliding scale and not even by a series of 

 steps, is extremely difficult, and must always remain unsatisfactory in 

 some particulars; but for convenience of reference, if for no other 

 reason, a classification of some sort is demanded, and various schemes, 

 which it is unnecessary here to enumerate, have been put forth to bridge 

 the difficulty. In all these schemes the primary divisions" are founded 

 upon the structure of the test as above described — that is, whether 

 chitinous, arenaceous, or calcareous, and whether perforate or imperfo- 

 rate. Beyond these distinctions, which seem to have a physiological 

 foundation, there is nothing upon which to base a classification but the 

 form of the test, which, as we have seen, is never determinate enough 

 to permit of the establishment of fixed boundary lines. Generic and 

 specific names of foraminifera, therefore, must not be considered as 

 having much zoological value, but only as convenient titles applied to 

 certain typical forms around which many varieties may be grouped. 

 And it must be remembered that, however elastic the definitions of 

 species, or even genera, there will often be a margin of doubt, and 

 the determination of j)lace in th« classification must be left to the 

 preference of the individual observer. 



A few words concerning the manipulation of material and specimens 

 may be of assistance to those beginning the study of the foraminifera. 



Collection of recent shallow- water forms may be made from shore 

 sands, from the anchor and chains, and especially from the " chain 

 lockers " of ships, from sponge sand, and by means of boat dredges from 

 the shallow waters of the coast. Deep-water forms are only obtainable 

 by special apparatus, such as is used in deep sea sounding or in purely 

 scientific explorations of the ocean bed. The specimens may be freed 

 from mud by the j^rocess of decantation — that is, repeatedly agitating 

 in water, and, after a very brief period to allow subsidence of the shells, 

 pouring off the turbid surface water. Or the material maybe put in a 

 bag made of fine bolting cloth and the bag shaken in a bucket of water. 

 The remaining foraminifera, mixed Avith more or less sand, pteropod 

 shells, sponge spicules, and debris of various sorts, should then be 

 thoroughly dried, bottled, and labeled. 



For examination of the dried material a dissecting microscope stand, 



