172 COMPARATIVE ANATOMY 



The reproduction of Bodo saltans is effected in the manner 

 usual among Protozoa, by binary fission. The plane of 

 division is longitudinal, and the process begins at the anterior 

 end and passes gradually to the posterior. The details of 

 nuclear division during fission have not been studied. It has 

 been said that the flagella share in the division, each being 

 split longitudinally into two, but this is doubtful. It is more 

 probable that the flagella are doubled immediately before or 

 during division. Tranverse fission, with division' of the trail- 

 ing flagellum only, has also been described. In addition to 

 binary division in the free swimming condition, a process of 

 encystment with subsequent spore formation has been de- 

 scribed, preceded by conjugation. It is said that a free swim- 

 ming form comes into contact with an anchored form and fuses 

 completely with it, the nuclei fusing as well as the cell-bodies. 

 The result of this act of conjugation is a zygote, a roughly 

 triangular body with a pair of flagella at each of two of the 

 angles. The zygote swims about awhile by its two pairs of 

 flagella, and then comes to rest, its nucleus having meanwhile 

 disappeared, and its protoplasm having become clear and 

 hyaline. After a period of quiescence the zygote bursts at its 

 three corners, and its contents escape as a mass of particles 

 so minute that they can hardly be seen with the best powers 

 of the microscope. These particles are known as spores, and 

 the observers who describe this method of reproduction allege 

 that they were able to follow the growth of these spores, and 

 to see them grow into small oval bodies which acquired first 

 a ventral flagellum, then a pointed extremity with an anterior 

 flagellum projecting from it, and finally by continued growth 

 in size arrived at the condition of an adult Bodo. This is the 

 only positive account of a process of conjugation followed by 

 spore formation in Bodo saltans. It has been seen only once, 

 by a pair of investigators working in concert, and, though their 

 observations are now many years old, they have never been 

 verified. Many authorities, indeed, are inclined to doubt their 

 truth altogether. It must be remembered, however, that the 

 difficulty of following the life-history of so minute and active an 

 organism as Bodo saltans is very great, and that one piece of 

 positive evidence on such a subject is of more importance than 

 any amount of negative evidence. A similar process of conju- 

 gation has been described in Bodo caudatus, but it is denied by 



