80 COLONIAL PROTOZOA 



spindle-shaped cells. These are the encysted stages of Monocystis. 

 Look for active stages. The latter are large, spindle-shaped cells, either 

 naked or surrounded by a layer of the earthworm's tissue from which 

 protrude the flagella of degenerating spermatozoa. Is the cell divided 

 as in Gregarinal Has it a nucleus? Are any structures visible which 

 can be interpreted as related to feeding? By reference to Fig. 39, 

 identify as many stages as your slide affords and draw the same ar- 

 ranged in order. 



COLONIAL PROTOZOA 



Exercise 1. — Types of Colonies. 



(a) Certain kinds of Protozoa remain attached to one another 

 after reproduction by cell division, thus producing colonies. In some 

 colonies the cells are connected by cytoplasmic processes ; in others the 

 individuals are held together by a non-living matrix W'hich they pro- 

 duce. Examine such colonial forms as may be available, preferably 

 in the living state. As some species are seldom found in cultures, it 

 may be necessary to study prepared slides. The following types of 

 colonies occur (Fig. 40): linear colonies, such as Ceratiuni] platelike 

 colonies, such as Gonium; arboroid colonies, such as Carchesium; 

 gregaloid colonies, such as Microgromia] and spheroid colonies, such 

 as Pandorina, Eudorina, Volvox, Spondylomorum, Synura, and Uro- 

 glena. Reference to charts or textbook figures will be helpful in 

 supplementing this brief study. 



Exercise 2. — Spheroid Colonies. 



(b) Study a series of spheroid colonies and compare them with 

 one another and with non-colonial forms such as Euglena, Chlamy- 

 domonas, and Chilomonas which are independent and hence physio- 

 logically balanced cells. Particularly in the flagellates with plantlike 

 characteristics, it is possible to arrange a series showing an increasing 

 number of cells and a progressive specialization, and thus division of 

 labor, among the cells of the colonies. For example, Gonium sociale 

 is a platelike colony consisting of four cells arranged in one plane and 

 held together by a gelatinous matrix; Gonium pectorale is a similar 

 colony composed of sixteen cells. In these colonies each cell is physio- 

 logically balanced, although the cells of any colony are held together 

 in the characteristic manner. Reproduction occurs by cell division 

 and by the syngamy of isogametes. Pandorina consists of sixteen 

 physiologically balanced cells forming a colony that is ovoid rather 

 than spherical in shape. Rei)roductiun occurs by cell division and by 



