1 66 MUCOR LESS. 



multiplication ; in Mucor the zygote remains inactive for a 

 longer or shorter time, and then under favourable conditions 

 germinates in much the same way as an ordinary spore, 

 forming a mycelium from which sporangium-bearing aerial 

 hyphae arise. A resting zygote of this kind, formed by the 

 conjugation of equal-sized gametes, is often distinguished as 

 a zygospore. 



Notice that differentiation of a very important kind is 

 exhibited by Mucor. In accordance with its comparatively 

 large size the function of reproduction is not performed by 

 the whole organism, as in all previously studied types, but a 

 certain portion of the protoplasm becomes shut off from the 

 rest, and to it — as spore or gamete — the ofifice of reproduc- 

 ing the entire organism is assigned. So that we have for 

 the first time true reproductive organs^ which may be of two 

 kinds, asexual — the sporangia, and sexual — the gametes.^ 



In describing the reproduction of Amoeba it was pointed 

 out (p. 20) that as the entire organism divides into two 

 daughter-cells, each of which begins an independent life, an 

 Amoeba cannot be said ever to die a natural death. The 

 same thing is true of the other unicellular forms we have 

 considered, since in the majority of them the entire organism 

 produces by simple fission two new individuals.^ But in 

 Mucor the state of things is entirely altered. A compara- 



' In Mucor no distinction can be drawn between the conjugating 

 body (gamete) and the organ which produces it (gonad). See the de- 

 scription of the sexual process in Vaucheria (Lesson XVI.) and in 

 Spirogyra (Lesson XIX.). 



^ An exception is formed by colonial forms such as Zoothamnium, in 

 which life is carried on from generation to generation by the reproduc- 

 tive zooids only. In all probability the colony itself, like an annual 

 plant, dies down after a longer or shorter time. Moreover the ciliate 

 infusoria are said, as already stated (p. 1 16), to sink into decrepitude 

 after multiplying by fission for a long series of generations. 



