i . PROTOZOA 19 



distinguished from the above in that one part (the bud) is smaller 

 than the other (the mother). The small size of the bud in most cases 

 makes possible the production of numerous buds on the surface of the 

 mother. This sort of reproduction is often found together with repro- 

 duction by fission in Ehizopoda, Heliozoa, Radiolaria, a few Gregarina, 

 Noctiluca, and Suctoria. 



In many forms reproduction by fission and gemmation are probably 

 preceded by a conjugation (temporary connection or fusing) or 

 copulation (permanent fusing) of two individuals. 



In many Protozoa, belonging to the most varied forms, the 

 individuals which are produced by fission or gemmation do not 

 separate entirely from each other, but remain more or less closely 

 connected, and so form colonies of unicellular organisms. 



These colonies are of the greatest importance, as they represent a 

 lower stage of the cell colonies of the Metazoa, and in many cases 

 reproduce in a manner which strongly reminds us of the sexual 

 reproduction of Metazoa and plants (see below). 



As an example of reproduction by gemmation we choose the Noctiluca, where 

 it occurs, probably after previous copulation of two individual Noctiluca, side by 

 side with simple reproduction by fission. The typical process is briefly as follows. 

 Gemmation occurs only in such individuals as have, when copulation has ended, lost 

 their organs of locomotion and mouths, and are thus simple globular bodies, on 

 the walls of which the chief mass of protoplasm (central plasm), with the nucleus, 

 is still to be found in its original place. The central plasm at this spot bulges out 

 somewhat, its nucleus divides by a kind of indirect fission, and the prominence at 

 the same time separates into two by a furrow. The division of the protoplasm is, 

 both here and in the following stages, merely superficial, since its deeper part remains 

 undivided. By continuous fission, 4, 8, 16, 32, 64, and up to 512 -nuclei arise, and 

 the same number of superficial prominences of protoplasm. Then each prominence 

 with its nucleus separates below the surface also from its neighbours and forms a 

 separate bud, on which a flagellurii and a peculiar process are developed ; this bud 

 leaves the mother animal as a spore (Fig. 11, b, c, p. 9). The further develop- 

 ment of these spores into young Noctiluca, has not yet been investigated. The whole 

 process of the formation of buds is very similar to the discoidal furrowing of the 

 meroblastie egg in the Metazoa, of which we shall speak later. 



Eeproduction by continuous fission and spore-formation is very 

 common among the Protozoa. In the latter case the whole body falls 

 to pieces, or else the greater part of it simultaneously dissolves into a 

 usually very large number of nucleated portions, i.e. spores. Both 

 these methods of reproduction are generally accomplished in resting 

 encysted individuals, and often after previous copulation or conjugation ; 

 this is especially the case with Gregarina and Flagellata. They may 

 occur together with ordinary reproduction by fission. The spores are 

 generally capable of free movement, occasionally amoeboid, or as 

 swarm spores they are furnished with a flagellum or several flagella 

 (Flagellata, Radiolaria, some Heliozoa, and Ehizopoda). Occasionally 

 (Gregarina) the spores themselves redivide, and only the portions thus 

 arising grow into adult animals. 



