360 Dr. H. M. Woodcock and Mr. G. Lapage. 



rule, it does not appear until the dumb-bell stage is reached, when it can 

 suddenly be seen projecting out from the side of the body, a short distance 

 from one end (fig. 23), and waving slightly to and fro. Occasionally, however, 

 it can be seen while the creature is still rounded (fig. 24), and in such a 

 case it may represent the old flagellum, which has been only partially 

 withdrawn. The constriction at the middle of the elongated body now 

 rapidly increases (figs. 25, 30), and about this time the second flagellum 

 appears, always some distance away from the first and in the other half 

 of the body, not far from the second nucleus. Very generally, the second 

 new flagellum projects out from the side of the body opposite that where 

 the first one is. The flagella increase in length and the body undergoes 

 little irregular, jerky movements. Its middle part becomes narrower and 

 more drawn out, the whole body having now the appearance of a double 

 pear. Usually the two flagella have their free ends directed towards the 

 middle, the bluntly rounded extremities becoming the anterior ends of the 

 two daughter-individuals ; though sometimes the second daughter-flagellum 

 (the later developed one) starts from near the middle of the body, i.e. 

 near to the constriction connecting the two halves, and points outwards. 

 Ultimately, helped by the movements of the flagella, the two halves of the 

 body are drawn still farther apart and the small daughter-individuals at 

 length separate, gliding away in opposite directions. The cytoplasmic " tail," 

 which each at first possesses, rapidly contracts and the typical body-form is 

 attained (fig. 31). 



In the above type of division, which is the most usual one, we regard the 

 cytoplasmic fission as being approximately transverse to the original long 

 axis, so that in this case we have the flagellate undergoing transverse division 

 of the body. The whole process is fairly rapid. From the time when an 

 individual has become ovoid and practically motionless to the time of 

 separation of the two daughter- individuals only 10 to 15 minutes usually 

 elapse. Now and again, however, the process is slower, taking upwards of 

 25 minutes ; but this is of rare occurrence. In such a case, moreover, we have 

 noticed that the body becomes divided before the second flagellum is formed, 

 so that one daughter-individual swims away, leaving the other motionless for 

 a few minutes longer, until it has developed its flagellum. 



On one or two occasions we have observed a modification of the above 

 method of division, a second flagellum being formed while the old one is still 

 present, having only been withdrawn (shortened) a little (fig. 32). The 

 shortening proceeds further (fig. 33), but in this case the old flagellum is not 

 entirely absorbed but forms the basis of one of the daughter-flagella. In this 

 variety of division we regard the fission of the body as being more in the long 



