362 



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



one, the two conjugating individuals were not very dissimilar. We leave the 

 matter there for the present, but hope to settle it before publishing our 

 detailed account.* 



Of course, the actual coming together and uniting is a matter of a few 

 seconds, and therefore difficult to catch ; but the gradual fusion of the two 

 gametes and the subsequent development of the zygote is a long process, and 

 we have observed every stage in it, on many occasions. The actual cyto- 

 plasmic union is lateral (fig. 40), and immediately after it has occurred one 

 would think that a single protoplasmic entity was now constituted. But 

 the subsequent behaviour is amazing and unique, so far as we are aware, in 

 the history of conjugating elements, and well illustrates the looseness of 

 the first , union and the fluidity of the protoplasm in Helkesimastix — and, 

 we doubt not, in other of these dung- and infusion-flagellates. As soon as 

 the actual cytoplasmic union lias occurred, the definite form of the two 

 gametes is practically lost, and there is for some time a remarkable lack 

 of attraction, or reluctance to unite, between the two essential parts, if 

 we may thus regard the nuclei and associated elements together with 

 the portion of cytoplasm immediately surrounding them. (This is probably 

 because the nuclei have not yet undergone a process of maturation.) We 

 cannot do better than describe the sequence of form-changes undergone by 

 the zygote immediately following the union, in the instance referred to. 



The conjugants of fig. 40 had not been joined for more than a minute or so 

 before they separated again in the anterior region, one individual being 

 desirous of steering off to the right, while the other preferred to keep 

 straight on (fig. 42). This little difference being composed and the two 

 individuals joined up again, one began to lag behind the other, the com- 

 bined body appearing now like an irregular rhomboid (fig. 43). The 

 conjugants were progressing forwards, more or less steadily, all the time. 

 In the next instant the smaller half had slipped still further back, and the 

 body had now the appearance of fig. 44. A few seconds later it was quite 

 behind the larger half (or individual), the two being connected together only 

 by a narrow cytoplasmic thread (fig. 45). After progressing thus for a short 

 distance the smaller half rapidly overtook the one in front by a kind of 

 " slithering " movement along it, and the protoplasm of both again joined 

 up along the side (fig. 46). A few seconds later a very characteristic 

 stage was reached, in which the combined body of the two conjugants 



* We have since reconsidered the above point and now think that the tendency to 

 adhere in couples in this way is probably purely a matter of surface tension or attraction. 

 We have observed the same phenomenon in observation-preparations of a non-conju- 

 gating strain of a closely allied species {vide p. 366, et seq.). 



