174 PROTOZOOLOGY 



ent individuals of a colony may either have protoplasmic connections 

 among them or be grouped within a gelatinous envelope if completely 

 separated. Or, in the case of loricate or stalked forms, these exo- 

 skeletal structures may become attached to one another. Although 

 varied in appearance, the arrangement and relationship of the com- 

 ponent individuals are constant, and this makes the basis for dis- 

 tinguishing the types of protozoan colonies, as follows: 



Catenoid or linear colony. The daughter individuals are attached 

 endwise, forming a chain of several individuals. It is of compara- 

 tively uncommon occurrence. Examples: Astomatous ciliates such as 

 Radiophrya (Fig. 298), Protoradiophrya (Fig. 298) and dinoflagel- 

 lates such as Ceratium, Haplozoon (Fig. 130) and Polykrikos (Fig. 

 132). 



Arboroid or dendritic colony. The individuals remain connected 

 with one another in a tree-form. The attachment may be by means 

 of the lorica, stalk, or gelatinous secretions. It is a very common 

 colony found in different groups. Examples: Dinobryon (Fig. 108), 

 Hyalobryon (Fig. 108), etc. (connection by lorica); Colacium (Fig. 

 121), many Peritricha (Figs. 362; 364), etc. (by stalk); Poterioden- 

 dron (Fig. 139), Stylobryon (Fig. 151), etc. (by lorica and stalk); 

 Hydrurus (Fig. 109), Spongomonas (Fig. 150), Cladomonas(Fig. 150) 

 and Anthophysis (Fig. 151) (by gelatinous secretions). 



Discoid colony. A small number of individuals are arranged in a 

 single plane and grouped together by a gelatinous substance. Exam- 

 ples: Cyclonexis (Fig. 108), Gonium (Fig. 116), Platydorina (Fig. 

 117), Protospongia (Fig. 138), Bicosoeca (Fig. 139), etc. 



Spheroid colony. The individuals are grouped in a spherical form. 

 Usually enveloped by a distinct gelatinous mass, the component 

 individuals may possess protoplasmic connections among them. 

 Examples: Uroglena (Fig. 108, c), Uroglenopsis (Fig. 108, d), Volvox 

 (Fig. 115), Pandorina (Fig. 117,/), Eudorina (Fig. 117, h), etc. Such 

 forms as Stephanoon (Fig. 117, a) appear to be intermediate between 

 this and the discoid type. The component cells of some spheroid 

 colonies show a distinct differentiation into somatic and reproductive 

 individuals, the latter developing from certain somatic cells during 

 the course of development. 



The gregaloid colony, which is sometimes spoken of, is a loose 

 group of individuals of one species, usually of Sarcodina, which 

 become attached to one another by means of pseudopodia in an ir- 

 regular form. 



