

PROTOZOA : FORAMINIFERA. 63 



ing no differentiation, or a very imperfect one, into ectosarc and 

 endosarc ; no nucleus or contractile vesicle ; pseudopodia filament- 

 ous, minutely subdivided, and inosculating freely to form a net- 

 work. * 



Section I. Imperforata. Envelope membranous or calca- 

 reous, the walls not perforated by apertures for the pseudo- 

 podia, which are emitted solely from the single or multiple 

 aperture of the shell. 



Families, i . Gromida. Test membranous. 



2. Miliolida. Test porcellanous. 



3. Lituolida. Test arenaceous. 



Section 2. Perforata. Envelope calcareous (hyaline or vit- 

 reous) or rarely arenaceous, its walls traversed by numerous 

 foramina for the emission of pseudopodia. 



The following classifications by D'Orbigny and Schultze are 

 founded merely upon the form of the shell, and, as such, are 

 purely arbitrary. Of the two, Schultze's arrangement is pro- 

 bably the more satisfactory. 



TABLE OF D'ORBIGNY'S ARRANGEMENT OF THE FORAMINIFERA. 



Order I. Monostega. Body consisting of a single segment; the shell of 

 a single chamber. 



Order 2. Stichostega. Segments arranged in a single row, in a straight 

 or slightly curved line. 



Order 3. Helicostega. Segments arranged in a spiral, the shell forming 

 a number of convolutions. (The "nautiloid " Foraminifera.} 



Order 4. Entomostega. Segments arranged on two alternating axes, 

 forming a spiral. 



Order 5- Enallostega. Segments arranged on two or three alternating 

 axes, not forming a spiral. 



Order 6. Agathistega. Chambers wound round an axis, each segment 

 embracing half the entire circumference. 



TABLE OF SCHULTZE'S ARRANGEMENT OF THE FORAMINIFERA. 



Section I. Helicoidea. Segments arranged in a convolute series. 

 Section 2. Rhabdoidea. Segments placed in a direct line. 

 Section 3. Soroidea. Segments disposed in an irregular manner. 



AFFINITIES OF FORAMINIFERA. The Foraminifera are re- 

 lated on the one hand to the Amcebea, and on the other to the 

 Spongida. From the former the " unilocular " Foraminifera 

 differ, both in the possession of an external envelope, and in 

 the much less highly differentiated characters of their sarcode ; 

 but the points of resemblance are obvious, and in such forms 

 as Actinophrys and Lieberkiihnia we are presented with an ap- 

 parent transition between the two orders. From the shelled 

 Amcebea, such as Arcdla, the Foraminifera are broadly sepa- 



