THE MASTIGOPHORA 263 



2. There is a single nucleus with its centrosome, and in addition one or 

 more blepharoplasts in relation to the flagellar apparatus. Then (a) at 

 division the old blepharoplasts and flagella are lost, and new blepharoplasts 

 arise during or after nuclear division from the centrosomes ; or (6) the blepharo- 

 plasts and flagella persist, and the former divide independently to form 

 daughter-blepharoplasts from which new flagella arise (Fig. 43). 



3. In a certain number of Flagellata, grouped provisionally as Haemo- 

 tiagellates or Binucleata (see next chapter), two nuclei, each probably possess- 

 ing its own centrosome, are present : a principal or trophic nucleus and an 

 accessory or kinetic nucleus. 



In Type 2 the blepharoplast attains to a greater or less degree of indepen- 

 dence of the centrosome, and divides independently of it for many generations 

 of ordinary vegetative reproduction by fission. But there are probably in 

 all cases periods in the life-cycle when the entire nuclear apparatus is reduced 

 to a single nucleus and centriole, from which the condition in the adult, 

 whatever it may be. arises. For the so-called fourth type of Hartrnann and 

 Ohagas (62), see below (p. 273). 



Reproduction and Life-Cycle. The commonest method of repro- 

 duction is simple or binary fission in the free state. The products 

 of the fission are of equal size, and the division of the body is in- 

 variably longitudinal (Senn, 358) that is to say, along an axis 

 continuing the direction of the principal flagellum or flagella. In 

 addition to this, the typical method of reproduction, other types of 

 division occur. Multiple fission in the free active condition is 

 known in some parasitic forms, such as Trypanosoma lewisi and 

 Lophomonas blattarum (Janicki, 70). On the other hand, fission 

 may sometimes take place in a resting, non-flagellated condition, or 

 within a cyst ; in the first case it is frequently, in the second 

 perhaps always, of a multiple type. 



The occurrence of syngamy in the life-cycle is a point which 

 has been disputed, probably owing to the fact that in forms of 

 simple structure it takes place only at long intervals in the life- 

 cycle, or under special conditions. Moreover, the longitudinal 

 division prevalent in this group makes it practically very difficult 

 to decide, except by continuous observation, whether two conjoined 

 flagellates are individuals about to fuse in syngamy or to separate 

 after fission. In the colonial Phytomonadina, where highly-differ- 

 entiated gametes are found, the occurrence of syngamy has long 

 been known, but the existence of sexual processes in other flagel- 

 lates has been doubted by high authorities. In recent years, how- 

 ever, it has been observed in a number of forms, and there can be 

 no doubt of the existence of sexual processes in flagellates generally. 

 A summary of recent observations, with full references, is given by 

 Dobell (335, pp. 109-111). The available data are as yet insufficient 

 to make it possible to give a connected account of syngamic pro- 

 cesses in Flagellata generally, and only a few typical cases can be 

 dealt with here. 



A simple type of syngamy has been described in Copromonas 



