34 OF THE RHIZOPODA IN GENERAL. 



an independent existence ; and yet so long as it remains in connection with the rest, it shares 

 a common life with them, the nutrient materials being introduced in the first instance through 

 the marginal segments, and being transmitted by protoplasmic circulation (ft 32 — 34) through 

 the entire mass. But in a large proportion of the polythalamous Foramiiiifera, the segments 

 thus successively formed are much more completely isolated from each other than are 

 those of OrUtolites ,• and there are several in which the chambers of the shell that 

 envelope these segments have so little connection with those that precede and follow 

 them, as to be easily detached from them and from each other. This is the case, for example, 

 with GlohigmiKc, and with many of the Nodosaria> ; and there is reason to believe that the 

 separation of their parts, which can be produced by very slight external violence, ma)' 

 be a means of their nudtiplication and diffusion. 



41. Besides this, which may be considered the mofst general method of reproduction 

 among Rhizopoda; other more special forms of that process are' indicated by observed facts. 

 In those types which exhibit, in the differentiation of "ectosarc" and " endosarc," and in the 

 presence of a nucleus, the nearest approach to the condition of cells, multiplication takes place, 

 as in growing cells generally, by a process of binary subdivision. This may often be witnessed 

 in ActinopJiri/s, round whose spherical body an annular constriction forms itself, which 

 gradually deepens so as to separate its two halves by a sort of hour-glass contraction 

 (Plate I, fig. 4) ; and the connecting band becomes more and more slender (fig. S), until a 

 complete separation of the two halves occurs. The process of fission, which may be completed 

 within half an hour from its commencement, seems to take place first in the contractile vesicle; 

 for each segment very early shows itself to be provided with its own (Fig. 4, v, v), and the 

 two vesicles are commonly removed to a considerable distance from one another. The 

 segments thus divided are not always equal, and sometimes their difference in size is veiy 

 considerable. — The like process of duplicative subdivision has been witnessed also in Amceba. 

 Whether in either case this subdivision commences in the nucleus, or extends through it 

 subsequently, has not yet been ascertained. 



42. It is affirmed by Schneider (xciii n) that Amccba sometimes passes into an encysted 

 condition. He observed it first to become globulai', and then to form a firm membrane on one 

 side, whilst the other portion maintained its peculiar character and actions. (In this state it seems 

 to have resembled the A. bilimbosa of Auerbach, Plate I, fig. 1 7.) By degrees the membi-ane 

 extended itself over the whole body, the moveable portion constantly becoming smaller, until 

 at last a completely closed cyst was produced, in the clear interior of which a round nucleus, 

 with a reddish halo, exactly like that of Polytoma and other Monadina, might be distinctly 

 observed. To what this encysting stage leads, there is at present nothing to show. — A 

 change which seems to be of the same nature has also been observed b)^ Schneider (xciii) 

 in BiJJfiif/ia, and by Schidtze (xcvii, p. 25) in Lagynis Baltica (Plate I, fig. 21, b). 



43. On the other hand, a junction of two individuals has been seen to take place in 

 Adinophrp, which has been supposed to correspond with the " conjugation '" of certain 

 Protophytes. It is very doubtful, however, if this junction or "zygosis " involves a complete 

 fusion of the substance of the bodies which take part in it; and there is not sufficient evidence 



