DESCRIPTIVE CATALOGUE OF RECENT FORAMINIFERA. 2f)3 



syiiiiuetry and complexity not surpassed by those of any testaceous 

 animals.'" 



From the resemblance of some of the shells of the foramiuifera to 

 those of the nautilus, they were for a long- time regarded as minute 

 cei^halopod mollusks; that is, aniong the highest of the invertebrates, 

 and it was not until the year 1835 that their true nature was discovered 

 and announced by M. Dujardiu to the French Academy of Sciences. 

 Since that time the study of this order of animals has been pursued by 

 able naturalists, and the results of their investigations appear in a 

 voluminous literature. Much yet remains to be learned of the life his- 

 tory of the animal, but its zoological position is established and its 

 importance in the economy of nature recognized. 



As fossils the foramiuifera are common in all geological systems from 

 the Devonian upward, but they are especially abundant in Mesozoic and 

 Cenozoic time. The chalk and many of the most extensive limestone 

 beds are formed principally of their remains. As to i)resent habitat, 

 their shells are found wherever dredgings are made, all over the ocean 

 tloor except in the polar regions. A few species are "pelagic;" that is, 

 they are found living at or near the surface of the water, but the weight 

 of evidence is in favor of the conclusion that the vast majority of them 

 pass all stages of life at the bottom, where they are found. In the 

 experience of the naturalists of the Albatross it was rare to find any 

 but the most minute and thin-shelled forms in the surface dredgings, 

 and still more rare for any to be taken in the "wing nets" that were 

 usually attached to the dredging apparatus. 



The living foraminifer is a minute bit of viscid, granular protoplasm, 

 without organs or tissues, without differentiation of substance into outer 

 membrane and inner contents, and in most instances without evident 

 nucleus or contractile vesicle. A nucleus has been recognized in a few 

 individuals, and hence this characteristic element of most living cells 

 is inferred to be present in all the members of the order. Like other 

 Rhizopods, it has the power to protrude any parts of its body as "pseu- 

 dopodia,"' for the purpose of locomotion or the prehension and absorption 

 of food. It differs, however, from the other Khizopods in that the 

 pseudoi^odia do not necessarily remain distinct, but flow together when- 

 ever they touch one another, forming sometimes an elaborate and 

 extended network of protoplasmic threads, which, however, may be 

 readily retracted and flow again into the body mass, leaving no indica- 

 tion of their previous existence. 



How the function of nutrition is accomplished and the nature and 

 condition of the organic material used as food by these minute animals 

 is not yet determined. Without doubt the pseudopodia are capable of 

 seizing and inclosing small organic particles with which they may come 

 in contact, and any part of the protoplasmic body, of which the pseudo- 

 potliaare but temporary extensions, is able to digest and assimilate the 



'Carpeuter, Intioductioii to the fetudy of the Foramiuifeia. 



