FLAGELLATA. 29 



Conjugation* is of very common occurrence. In certain small 

 Itodoninai it takes place between several individuals in the amoeboid 

 state, so as to give rise to a plasmodium, which, as in the Mycetozoa, 

 encysts and ^divides into spores. In Cercomonas the gametes become 

 amoeboid and conjugate in pairs. Sometimes the gametes, or one 

 of them, differ in size or history from the ordinary forms. In the 

 Clilainydomonadina small forms (inicrogametes or microgonidia) often 

 arise by fission and conjugate with similar inicrogametes or with the 

 ordinary form, or with forms which have been produced from the 

 ordinary form by a smaller amount of fission. In Polytoma gametes 

 are produced by tetrapartite fission, and are all alike. 



The differentiation of the gametes is carried furthest in some of 

 the Volvodna. In Volvox both gametes are specially differentiated 

 individuals of the colony. The megagamete or macrogonidium is 

 an ovum-like cell without nagella, while the microgamete or micro- 

 gonidium is a small flagellated organism produced by fission from the 

 ordinary form. In some species these two kinds of gametes are not 

 found in the same individuals, so that there are unisexual colonies. 

 The zygote resulting from their conjugation secretes a thick membrane, 

 and remains in the resting state for some time. On the death of the 

 mother it falls to the bottom, and when conditions are favourable 

 it develops into a new colony. 



Conjugation is, so far as is known, followed by encystment, the 

 zygote remaining for some time quiescent. While in this condition 

 it is capable of resisting drought, which indeed seems to be favourable 

 to it. When placed in suitable conditions the contents of the cyst 

 divide into two or four parts, which issue as young forms to begin 

 a new cycle of life. The breaking up of the zygote into minute 

 spores is only described for a few forms (Dallinger, Bodo, Tetramita). 



The Flagellata are allied to the Gymnomyxa by such forms as the Monadina, 

 in which the amoeboid condition may occur as an important phase in the life- 

 history, and by those of the Gymnomyxa in which the young leave the spore-case 

 in the flagellate form (mastigopod). In other words the Flagellata and Gymno- 

 myxa agree with one another in including forms which pass through both the 

 myxopod and mastigopod condition in the life-history, the difference between 

 these forms consisting mainly in the relative duration of the two states. 

 Paramceba, a form recently described by Schaudinn (Sitzb. K. Preuss. Akad. W., 



* Klebs throws doubt upon the occurrence of conjugation in any true 

 Flagellate. He admits that it takes place in the Volvodna, which he removes 

 from the Flagellata, and in certain other forms such as Cilioplirys and Protomonas, 

 all of which he refers to the Heliozoa; but more recently Dill (Jahrb. wiss. 

 Bot., 28, 1895) has not only stated that transverse fission occurs, but also that 

 gametes are formed in Chlamydomonas, which is a member of the Flagellata. 



