430 SECOND PART. MVCETOZOA. 



formation of the spores and of the capillitium which in many genera accompanies the 

 spores. These processes also have been most thoroughly and satisfactorily examined 

 in the lime-containing Physareae, Rostafinski's Calcareae, and will be described from 

 them in this place. 



In the simpler cases of forming of sporangia, which we may examine first, either 

 an entire plasmodium spread out on its substratum becomes transformed into a 

 sporangium, or it divides into a number, often a large number, of pieces, each of 

 which suffers transformation. This transformation is the result of the same kind of 

 amoeboid movement of the protoplasm as that which causes the change of shape and 

 place in the vegetating plasmodium, with the difference only that in the forming 

 of sporangia the masses of protoplasm by drawing in their branches become 

 constantly broader and rounded off and at length assume stable forms. The spor- 

 angia which lie flat on their substrata are in conformation simply portions of a 

 plasmodium which have been thus contracted and thickened. Erect sporangia on a 

 narrow or stalk-like base begin as node-like swellings on a branch of the plasmodium, 

 and gradually rise to their ultimate form as the surrounding protoplasm flows into 

 them and assumes an upward direction. 



The soft envelope which surrounded the retracted branches of the plasmodium 

 remains sticking to the substratum and there dries up ; but there appears in its place 

 round the young sporangium a firm membrane evidently produced by its further 

 growth, and this membrane constitutes the wall of the sporangium which often grows 

 to a considerable thickness. In the stalked forms the sporangium-wall begins to 

 strengthen and get firm at the base of the stalk, and the process advances upwards. 

 The zones of the membranes successively growing stronger serve as a support for 

 the upward moving protoplasm. 



During the forming of the sporangia the solid ingesta which are present in the 

 plasmodium begin to be expelled from it. When a sporangium has assumed its 

 definitive form the spore-plasm is separated off inside it. The granules of calcium 

 carbonate, the pigment and perhaps other substances also, which at present are not 

 precisely determined, are eliminated from the true protoplasm. In Physarum and its 

 nearest allies they move to the wall and become imbedded in it or attached to it ; or 

 they collect into lumps of various shapes which are arranged differently inside the 

 sporangium in different species, and by the formation of a membrane round them 

 are soon converted into vesicles containing calcium carbonate or pigment (Fig. 191). 

 In Didymium and the forms nearest to it the calcium carbonate granules in the plas- 

 modium are dissolved and in this state are expelled from the sporangium, and while 

 the granules disappear inside, the outer surface becomes covered with crystals of the 

 salt. In Didymium Serpula the only well-known species of this group with coloured 

 plasmodia, the yellow colouring matter is gathered up at the same time inside the 

 sporangium into round lumps, which are then inclosed in pigment-vesicles by the 

 formation of membranes round them. The protoplasm which remains after these 

 substances have been removed from it is for the most part a colourless body with small 

 granules uniformly distributed through it. By staining numerous nuclei are made 

 visible in it. This plasm has been termed spore-plasm, because much the larger part 

 of it is used for forming spores; as soon as it has got rid of the foreign substances in it 

 its nuclei rapidly increase in number, and at length the whole mass divides simul- 



