48 THE FORAMINIFERA 



Each of the characters by which the group is defined loses in 

 distinctness when followed into this borderland region. The shell, 

 which attains great complexity in the higher forms, is membranous 

 in many of the lower, and in Lieberkiihnia, Diplophrys, and Myxotheca 

 (Fig. 2) can hardly be said to exist. In Hyalopus the pseudopodia, 

 though branching and pointed, do not anastomose with one another 

 (Fig. 15), and in several of the fresh- water Gromiidae few anasto- 

 moses are found. The filiform nature which distinguishes the 

 pseudopodia of the Foraminifera from the blunt-ended pseudopodia 

 of the Lobosa is a better defining character; but in view of the 

 close parallel which, as will be explained below, the life -history 

 of Trichosphaerium, a member of the Lobosa, appears to present with 

 that of many Foraminifera, its importance in a natural classification 

 may be doubted. 



A few of the simpler forms live in moor pools and other fresh 

 waters, but the great majority are marine. Most of these are 

 littoral in habitat ; many extend their range to the floors of the 

 deep oceans ; while a small group, few in the number of species, 

 but very abundant in individuals, lead a pelagic existence. 



The Protoplasm presents a uniform character without any obvious 

 separation into an outer and inner layer of different refracting power. 

 It is finely granular throughout, and coarse granules are usually 

 present in the protoplasm contained within the test. 



The pseudopodia in some of the lower forms are long and root- 

 like, and extend to great distances, giving off branches in their course, 

 and to such forms Dujardin's name Rhizopoda is especially appro- 

 priate ; but most members of the group are characterised by pseudo- 

 podia of a different nature (Fig. 1). They are for the most part 

 very slender, and spread from the neighbourhood of the aperture 

 or apertures of the shell in fan-like or sheaf-like groups. The outer 

 surface of the shell is invested by a layer of protoplasm, and from 

 this also groups of pseudopodia originate. 



The pseudopodia frequently branch and anastomose in their 

 course, and between the points of union of the reticulum which 

 they form, they generally run straight, owing in part to the tension 

 which they mutually exert on one another. Some of the radiating 

 strands form broad bands, branching peripherally, but the majority 

 are exceedingly slender, and the ultimate branches are of extreme 

 tenuity. At the points of union broad expansions of protoplasm 

 are often formed. The network of pseudopodia is in part projected 

 free in the water, in part applied to surrounding objects, and 

 serves at once for the prehension of food, as a peripheral sensory 

 apparatus, and as a means of attachment and of locomotion. 



When a strand of the reticulum is attentively examined, the 

 granules contained in the protoplasm are seen to hurry along its 



