SARCODINA 



67 



Order FORAMINIFERA 



Sarcodina which have either a shell or reticulate pseudopodia or, 

 usually, both these features; and in pelagic species a vacuolated 

 outer layer of protoplasm. 



The shell may be of one or of several chambers, and is composed 

 in different cases of different materials, nitrogenous, calcareous, 

 siliceous, or of foreign particles. 



The pseudopodia may be lobose, filose, reticulate without streaming 

 of particles along them, or reticulate with streaming. The latter type 

 alone is found in the Polythalamia. 



A SCO 



Fig. 58. Binary fission of Euglypha alveolata, x about 450. From Hegner 

 and Taliaferro, after Schewiakoff . A, B, C, D, Successive stages in the mitosis, 

 with formation and occupation of a new shell. 



The reproduction of the single-chambered forms (Monothalamia) 

 is both by binary and by multiple fission. In binary fission, Lie- 

 berkiihnia and Trichosphaerium divide the shell. In the rest, a portion 

 of the protoplasm emerges from the old shell and secretes a new one 

 (Fig. 58), the nucleus or nuclei divide, one of the products of each 

 passing into the protruded protoplasm while the other remains in the 

 old shell, and the two portions of protoplasm break apart. Multiple 

 fission usually produces amoebulae, sometimes flagellulae. The latter 

 are known or suspected to be gametes. In this group there does not 

 usually appear to be a regular alternation of sexual and asexual 



5-2 



