38 



BIOLOGY OF THE PROTOZOA 



plasm. New shells are deposited about the buds and chambered 

 individuals result (Fig. 19). Repetition of the process gives rise to 

 distinct types of polythalamous or many-chambered Foraminifera, 

 depending upon the position assumed by the bud (Nodosarine, 

 Frondicularian, Rotaline types, etc.). 



Dogiel (1929) interprets the duplication (polymerization) of 

 organelles such as contractile vacuoles, macro- and micronuclei, 

 flagella groups, particularly of Polymastigida, somatella formation 

 (see p. 233), multiple nuclei and kinetoplasts of Calonymphidae 

 (see p. 115), etc., as evidence of gradations in cellular differentia- 

 tions in Protozoa leading to a multicellular condition which is fully 

 established in Metazoa. 



I D V 



Fig. 19. — Types of shells of Foraminifera. A, B, side and ventral aspects of Cornu- 

 spira sp. ; C, and D, types of Nodosaria. (After Carpenter.) 



In colonial types the form of the aggregate is determined by the 

 manner in which the individuals are held together after division. 

 The different types are described as spheroid, catenoid, arboroid 

 and gregaloid colonies. In the majority of spheroid colonies, the 

 associated cells are held together by a gelatinous matrix secreted 

 by the individual cells. The typical form of such colonies is spher- 

 ical as in the genus Proterospongia, among the flagellates, or Ophryd- 

 ium versatile among the ciliates. In catenoid colonies the individuals 

 are attached end to end as in some species of ciliates (e. g., Hapto- 

 phrya), or side by side as in the flagellate Rhipidodendron. In 

 arboroid colonies the individuals are attached by longer or shorter 

 stalks in a branching, often bush-like colony [Clathrulina elegans, 

 Poteriodendron petiolatum (Fig. 139, p. 418) , Codosiga eymosa (Fig. 20), 

 Epistylis umbellaria (Fig. 143, p. 280), Carchesium polypinum, Zooth- 

 amnium arbusctda, etc.] In the majority of these arboroid colonies 

 each individual is borne on its own stem which branches from a 

 common stalk. In some cases, however, especially amongst the 

 flagellates, each stalk bears a cluster of individuals as in Cladomonas 



