THE SARCODINA 71 



relationship between the symbionts was worked out by Cienkowsky, 

 Brandt, Haeckel, and Entz, the latter noting that the plant-cells are 

 invariably found just outside of the endoplasm, where they do not 

 come in contact with endoplasm and its digestive fluids. According 

 to the more recent observations of Le Dantec ('92), however, the 

 digestive fluid of these animals is unable to dissolve the cellulose 

 membranes of the plant-cells, and they remain uninjured in the endo- 

 plasm, dividing there when the conditions are favorable. 



D 



A. SHELLS AND TESTS 



The ectoplasm of naked protoplasm shows a tendency to condense 

 or stiffen when in contact with water, and a cuticle or membrane is 

 the result. Amceba proteus, with its differentiation into endoplasm and 

 ectoplasm, shows a primitive stage in the development of such mem- 

 branes. Here the ectoplasm remains plastic enough to yield to the 

 inner pressure of the organ- 

 ism and to form the first 

 part of every pseudopodium ; 

 it is rapidly pushed aside, 

 however, and the endoplasm 

 becomes the advancing part. 

 In Amoeba tentaculata the 

 outer layer has become more 

 firm and the pressure from 

 within expends itself upon 

 pseudopodia which are pro- 

 truded through permanent 

 holes (Fjg. 12, A). The 



membrane may become Still Fi 8- 35- Types of marine rhizopod shells (Reticula- 



r. ., , rlida. [CARPENTER.] 



more firm through the ^ Lateral B Vent L ra] view of a j monothalamous 



deposition Of Chitin, Until, shell (Cornuspira foliacea Phillips). C. A simple poly- 



as in the radiolarian central thaiamous shell 

 capsule, it is an efficient 

 means of protection. In addition to the chitin, certain Sarcodina 

 secrete a silicious mucilaginous material, which, like the chiti- 

 nous cement, is frequently the means of gluing together not only 

 regular plates or disks which the organism also secretes, but foreign 

 particles of various kinds. The tests thus made may be entirely of 

 lime, as in the Reticulariida, or of silica, as in the Radiolaria and 

 many of the Heliozoa, or of sand crystals, diatom-shells, or detritus of 

 various kinds. 



In the lime-shells (Reticulariida or Foraminifera) the secretion of 

 calcium carbonate, except for the invariable presence of a mouth- 



D. Verte- 



bralma sp., a fossil form. 



