28 Dr. F. Bloclimann on the 



tion upon this occasion which, when followed out, led to 

 results which were of some interest, and these I describe in the 

 following pages. They may in some respects serve as a sup- 

 plement to Gruber's beautiful investigations *, by which the 

 process of division in the shell-bearing freshwater Rhizopods 

 was first thoroughly elucidated. 



As is well known, the process of division runs as follows : — 

 In an animal which has already formed the necessary shell- 

 laraellse in its interior the protoplasm is protruded from the 

 orifice in the form of a small bud covered with shell-laraellai. 

 This flowing forth of the plasma continues until the mass 

 outside the original shell, now covered with the new shell- 

 lamellge, has attained the same volume and the same shape as 

 the original animal. During this process the nucleus also 

 divides and one half of it passes into the newly produced 

 individual, so that in this way two perfectly similar animals 

 are produced, and these soon separate from each other to live 

 as individual animals. 



However, the separation of the animals thus produced does 

 not always occur ; but by no means unfrequently we may 

 observe a very remarkable process, by which, while it is true 

 that two shells and two nuclei are produced, only a single 

 animal proceeds from such a division. 



Thus after the division has taken place quite normally and 

 the nucleus of the newly formed individual has occupied its 

 ordmavy position at the bottom of the new shell, the proto- 

 plasm is retracted out of the newly formed shell (PI. IV. 

 fig. 1), still, however^ remaining attached to the bottom of the 

 shell, so that from this point a comparatively thin cord stretches 

 towards the aperture along the axis of the shell, passing 

 about in the middle of the shell into a larger mass of plasma. 

 The greater part of this cord appears quite hyaline, containing 

 only extremely fine granules ; this is caused by the position 

 here of the nucleus (n^), which has now become nearly cylin- 

 drical. 



In the principal mass of the plasma, especially between the 

 two orifices now pressed close together, active flow-pheno- 

 mena are observable, just such as were also observed by 

 Gruber during division. Upon continuing the observation it 

 is seen that the cord in the new shell is drawn out into a thin 

 thread, while the nucleus again acquires its regularly spherical 

 form (Hg. 2). 



This thread is now seen to become alternately thicker and 



* " Der Tlieiluugsvorganj? bei Euglypha alveolata," in Zeitschr. fiir 

 •wiss. Zool. Bd. XXXV. pp. 431-430 (1881j. See ' Annals,' ser. o, vol. ix. 

 p. 13'). 



