246 THE PROTOZOA 



Each primary cyst then divides into two secondary cysts, which 

 after nuclear reduction become the gametes and copulate. The 

 zygote develops into a young Actinosphcerium with several nuclei, 

 which emerges from the cyst and begins a vegetative life, but appears 

 to divide frequently at the start into uninucleate, Actinophrys-Mke 

 forms. 



In other genera, on the other hand, and especially in those of the 

 Acanthocystis - type (Acanthocystis, Clathrulina, and Wagnerella), 

 flagellate swarm - spores are formed, which probably represent 

 gametes, as in many other Sarcodina. 



The life-history of Wagnerella has recently been studied in detail by 

 Zuelzer (86) ; her investigations reveal a diversity in its modes of reproduction 

 almost as great as that seen in Arcella, and indicate that there is much yet 

 to be discovered with regard to the life-cycles of other forms. 



Wagnerella exhibits, according to Zuelzer, dimorphism correlated with 

 alternation of generations. In June and July stout forms are observed, 

 which are believed to arise from the conjugation of gametes ; they reproduce 

 by binary fission, and by a process of schizogony giving rise to amcebulae 

 (agametes). The more usual form, on the other hand, is smaller and more 

 slender, and multiplies by binary fission, gemmation, and formation of 

 flagellate swarm-spores. Hence this peculiar form reproduces in a variety 

 of ways. In the process of binary fission the nucleus migrates from the 

 base up the stalk into the head, and places itself beside the central grain, 

 which divides, its two halves passing to opposite sides of the nucleus ; then 

 the nucleus follows suit and divides also. Divisions of the central grains, 

 and subsequently of the corresponding nuclei, may be repeated until eight to 

 ten nuclei and as many central grains are present. Each nuclear division 

 is followed by division of the head, at first incomplete, so that a condition 

 results resembling the colonial form Rhaphidiophrys, a number of daughter- 

 individuals united together, and each sending out pseudopodia (Fig. 102, D). 

 After a time the colony breaks up, the daughter-individuals separate, and 

 each one fixes itself and grows into the adult Wagnerella-form. 



Bud-formation in Wagnerella (Fig. 102, A C) is initiated by division 

 of the karyosome within the nucleus, which retains its position in the base. 

 The process is repeated until the nucleus contains a number of karyosomes, 

 each with a centriole. The nucleus then buds off one or more small daughter- 

 nuclei, each containing a single karyosome. Sometimes the nucleus breaks 

 up entirely into as many daughter-nuclei as there are karyosomes, in which 

 case the parent-individual dies off, in a manner similar to Arcella (p. 180), 

 after liberation of the buds. Each daughter-nucleus migrates up the stalk 

 into the head, where it becomes surrounded by a layer of protoplasm to form 

 the bud, which is set free at first as an amoeboid body. Before or after being 

 set free, the bud may multiply by binary fission with mitosis, in which the 

 centriole in the karyosome acts as a centrosome. Finally each amoeboid 

 body develops into a Wagnerella, and in the process the centriole passes out 

 of the nucleus and becomes the central grain, while the nucleus becomes 

 displaced from the centre. In the process of gemmation the central grain 

 of the parent-individual takes no share whatever. 



In the formation of the swarm-spores, minute secondary nuclei arise from 

 chromidia near the principal nucleus in the base. Each secondary nucleus 

 forms a centriole and divides by mitosis ; the division is repeated until the 

 whole body, stalk and head as well as base, is filled with small nuclei, while 

 the primary nucleus degenerates. The body then divides up into as many 

 cells as there are secondary nuclei, each cell becoming a biflagellate swarm- 

 spore which is set free, while the parent -individual degenerates. The destiny 

 of the swarm-spores is uncertain, but they are believed to be gametes. 



