SPECIAL MORPHOLOGY AND TAXONOMY OF SARCODINA 339 



Order 2. Testacea. 



These forms are generally described as amoebae with shells; by 

 some they are grouped as a subdivision of the Foraminifera (Doflein). 

 The protoplasmic and test structure, as well as the pseudopodia are 

 so different from Foraminifera that little is gained by this pro- 

 cedure, while the association with naked forms has a long historical 

 backing. They are almost exclusively fresh-water forms, although 

 some species are represented in brackish water as well. iNIany 

 species are semiterrestrial and abound in moss and similar damp 

 places. The protoplasmic body differs from that of the Amoebidse 

 in having the ectoplasm concentrated at the region of the shell 

 opening, while many forms show a distinct zonal differentiation of 

 the protoplasm. Contractile vacuoles are always present. 



Nuclei are either single, double or multiple and are usually accom- 

 panied by a zone of chromidia in the form of a dense reticulum 

 from which, according to the observations of numerous observers, 

 the nuclei of gametes are formed (Schaudinn, Zuelzer, Elpatiewsky, 

 et ah). It is rather the fashion to doubt this interpretation on the 

 ground that such nuclei are probably parasites, but we shall adhere 

 to. it until the critics have a more probable ex])lanation of the 

 nature of the chromidia (p. 4S). 



Pseudopodia are filopodia which in a few instances, have the 

 tendency to branch. They lack the medullary endoplasm of lobo- 

 podia and have a considerable power of independent movement. 



The tests are simple, one-chambered structures of widely-varied 

 form, frequently ornamented with spines and processes. The basis 

 of all shells is a pseudochitinous membrane which, in some forms 

 is greatly thickened and constitutes the test; in other cases foreign 

 particles are cemented to the outside of the chitinous membrane 

 (Difflugia, Centropy.ris, etc.), and in still other cases silicious plates 

 are precipitated in the endoplasm in the vicinity of the nucleus, and 

 deposited on the chitinous membrane in definite patterns character- 

 istic of different genera {Euglypha, Quadnda). 



Reproduction occurs by longitudinal binary division in forms with 

 a soft chitinous membrane, where membranes di\ide with the soft 

 body; in other cases it occurs by so-called "budding division" 

 whereby the protoplasm swells out of the shell mouth to form a bud 

 which assumes the size and shape of the parent (p. 217). Multiple 

 division also occurs in some types; many nuclei are formed by 

 division; these become the nuclei of small naked amoebae which 

 after a short period of free movement and growth secrete the shell 

 characteristic of the species. Fertilization processes have been 

 described for several types {Centropyxis, Arcella, TrichosphcBrium, 

 Difflugia, etc.), the gametes being either amoebula? or flagellulae. 



