THE MASTIGOPHORA 131 



ing attached to the stalk by their basal ends. In Dinobryon, a free- 

 swimming colony of variable size, each monad occupies a small cup 

 of cellulose (see Fig. 61). They increase by simple longitudinal 

 division, one daughter-cell remaining in the original house, while the 

 other moves out to the edge of the parent cup, where it attaches itself 

 by the posterior end. A cellulose cup is then secreted about the 

 daughter-cell, remaining firmly attached, however, to the parent cup. 

 The mother-cell may divide again and again, the daughter-cells at- 

 taching themselves to the edge of the cup already formed until there 

 are three or more individuals around the edge of the original one. 

 At the same time the daughter-cells may be dividing in a similar 

 manner, and a much-branched bush-like colony is the result. Other 

 forms have stalks which in some cases are much longer than the in- 

 dividuals themselves (Codonocladium, Dendromonas, Codonosiga, etc.). 



Still another type of colony-formation is found among the Dino- 

 flagellidia, where from two to eight individuals are connected end to 

 end by their shell processes (Ceratium). The significance of this 

 chain-formation (catenation) is not clearly established, many regard- 

 ing it as the result of incomplete division (Pouchet, '85), others as 

 preparatory to conjugation (Butschli, '83). 



The colonies as well as the individuals may increase by division, 

 a purely mechanical process, however, and probably due to the un- 

 wieldy size of the overgrown aggregate. Zacharias ('95) and others 

 have seen large colonies of Uroglena break into two portions through 

 the asynchronous action of flagella in different regions. If the 

 flagella of one half of the colony vibrate in one direction while those 

 of the other half vibrate in an opposite direction, the result is a twist- 

 ing of the entire mass which must ultimately give way. Such division 

 cannot be regarded as reproduction in a strict sense. 



Closely allied to simple division is the formation of swarm-spores or 

 microgonidia. This may occur either in the free motile condition as 

 in Polytoma or Chlorogonium, or in the encysted and protected state, 

 as in many Monadida. The simplest form is seen in such cases as 

 Polytoma, where, instead of dividing into two portions, the organism 

 divides into four, eight, or, according to Dallinger and Drysdale, into 

 sixteen smaller forms. These develop new flagella, make their way 

 through the parent membrane, and grow to full size. The formation 

 of similar gametes has been observed in most of the Mastigophora, 

 either in their resting or in their encysted stages. The flagella are 

 drawn in, a mantle or cyst is secreted, within which the protoplasm 

 divides into a number of spores. In some cases swarm-spores, like 

 those of the Radiolaria, are of different sizes (macro- and micro- 

 gametes), and these may conjugate. 



So far as known, the formation of gametes is not accompanied by 



