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



the two essential portions, since the cytoplasm is apparently indiscriminately 

 divided at times — is not at all an exceptional occurrence ; indeed, we 

 think something similar usually happens during the earlier stages of 

 syngamy. On other occasions we have seen both the " slithering " of two 

 slightly unequal portions and the almost complete separation of the two 

 halves which remained connected only by a delicate thread, just as in the 

 above case. The joining up again in such a case occurs, we consider, as a 

 result of the rapid contraction of the connecting thread, in just the same 

 manner as the lagging portion of protoplasm was suddenly hauled up into the 

 main body of the Ccrcdbodo (cf. above). Further examples of these early 

 conjugation stages are given in figs. 54-57, from different zygotes. Even 

 after the banner has been definitely formed for as long as an hour, we have 

 seen it suddenly break down into two portions, one behind the other. 



Different forms assumed by the banner, when at length permanent, are 

 seen in figs. 58-62. As time goes on the banner gradually loses its square 

 shape and becomes oblong (fig. 63), the two parallel flagella also gradually 

 coming to lie nearer to the mid-dorsal line, and so to each other. Most 

 probably, by this time, the maturation processes of the gamete-nuclei are 

 completed. Further, the two flagella are slowly shortening in length. In its 

 earlier period, however, the banner is still capable of performing the active, 

 undulating (free) movement, as well as the more characteristic gliding move- 

 ment. From an oblong the banner now turns to an oval — really, of course, 

 to an ovoid — which is ultimately almost as deep as it is broad. We have 

 followed a banner from the time when it had about just become permanent 

 (e.g. as in figs. 61 and 62), up to the definite oval (fig. 65), the time occupied 

 being about three hours. In an observation-preparation in which syngamy 

 has been going on for some time, banners and ovals are quite numerous ; this 

 will be apparent when it is remembered that every cyst formed is a zygote- 

 cyst. At a later stage the two flagella have become much shorter (figs. 66 

 and 67), and the flagellate moves very sluggishly ; it soon ceases to displace 

 itself and only performs little turning and "knicking" movements. The 

 protoplasm becomes contracted and somewhat denser, and the oval nearly 

 always leaves the under surface of the cover-slip by this time and sinks to the 

 lower level of the medium. The flagella are at length quite absorbed and the 

 body becomes spherical. We have followed an individual oval with two 

 flagella close together, as in fig. 65, up to the time when it became a motion- 

 less, rounded body at the lower level, and this change took about six hours. 

 The whole process up to this stage takes from 9 to 10 hours, according to our 

 actual observations ; of course, this may not be the minimum period required, 

 though we should say it is not far from it. 



