336 



Rev. W. H. Dallinger on 



[May 2, 



Great vigour of movement now ensues, but of an irregular kind ; and 

 instead of being forward, is from side to side ; when suddenly the 

 distance between the two parts widens, as in fig. 8, a stretched fibre of 

 sarcode alone uniting them. Movement is still apparently concerted, 

 and is from each other, the fibre of sarcode becoming speedily thinner 

 until it has stretched to double the length of an ordinary trailing 

 flagellum ; this is shown in fig. 9 ; and in a few seconds more, by a 

 vigorous movement of each body in opposite directions, as the arrows 

 indicate, the fine filament of sarcode snaps in the middle, and two 

 perfect forms are thus set free by fission. 



The process is carried on with great vigour, and is' apparently the 

 only metamorphosis to which the organism is subject. In nine separate 

 cases a single form was carefully followed, that is to say, a vigorous 

 form in each case was watched from its first act of fission ; one part of 

 the divided organism being constantly followed. The whole process of 

 division, from its visible beginning to its close, took place in from four 

 to seven minutes ; and was recommenced during the first hour in periods 

 not exceeding three minutes. For the next two hours the intervals 

 would be from seven to ten minutes, and after this the intervals became 

 indefinite, not being less than twenty nor more than forty minutes. 



Following the first separated segments, as represented by one part of 

 its divisions, in all its subsequent separations, as begun and carried on 

 by nine separate organisms in which fission happened for the first time, 

 the terminus of the process of fission in the last of the segment-forms in 

 all the cases, was death in six of the nine instances, and entire metamor- 

 phosis in the remaining three. In the cases in which death ensued the 

 process of fission was continued for seven hours in one case ; six hours 

 in three cases; and five-and-a-half hours in the remaining two. In 

 the cases in which metamorphosis took place, three hours in one case, 

 and four hours in the remaining two, terminated the period of fission. 

 There was then inaction in this last segment-form, and the appearance 

 indeed of the loss of vitality ; but the first indication of a difference be- 

 tween this and the more frequent cases of vital collapse, was the rapid 

 " clubbing," or gathering into knots of the trailing flagella, followed by 

 a rapid enlargement of the nucleus, and a glittering, rapidly amoeboid 

 condition of the entire body. This condition is shown in fig. 10. The 

 changes are now very rapid : not more than seventy seconds elapse 

 before the trailing fiagella are wholly fused with the body substance, 

 and while the head-and-neck-like protuberance pointed out in fig. 1, 

 is preserved, the body, having lost the lateral or trailing flagella, 

 becomes oval; with an immensely developed nucleus, as shown in 

 fig. 11. It swims now with great ease, but always merely in a 

 straight line, and always takes a sudden dart backwards before 

 changing the direction of its motion. It may swim in this way for 

 from a quarter to half an hour ; but during this time a band of gra- 



