426 NATURAL SCIENCE. June, 1895. 



exhibit characters that suggest affinities with both the animal and 

 vegetable kingdoms. Many persons see in them a hint of the 

 primitive appearance of living matter. The life-history of a slime- 

 fungus may be taken as beginning with a spore enclosed in a firm 

 cell-wall. In suitable surroundings the cell-wall bursts and there 

 creeps out a tiny " swarm-spore," a little naked mass of protoplasm 

 with a contractile vacuole and a nucleus, and provided with a single 

 flagellum or cilium. In this stage the little cell wriggles through the 

 water, in its appearance and in its method of feeding being quite like 

 an animal. In this stage, too, it multiplies rapidly by division. The 

 numerous swarm-spores thus produced become amoeboid ; instead of 

 being rowed through the water by the lashing movements of a cilium, 

 they creep through it by the protrusion of pseudopodia. In this 

 condition they are to be found chiefly where there are decaying, 

 comparatively solid, masses of organic matter. The amoebae fuse 

 together, forming a plasmodium, in which the outlines of the original 

 amoebae sometimes remain visible, sometimes are lost. The whole 

 Plasmodium creeps about and exhibits streaming movements like a 

 gigantic amoeba. Such a plasmodium offers, from its size, many 

 facilities for the investigation of protoplasm in the mass, and a 

 number of remarkable experiments have been performed upon the 

 Plasmodia of various species showing the positive and negative 

 attraction between the protoplasm and various chemical substances. 

 Into these general biological questions Mr. Lister, of course, does 

 not enter, as his monograph is chiefly systematic. 



The plasmodium contains a number of nuclei, and these may 

 multiply. After a time, especially when the substance upon which 

 the plasmodium is creeping becomes dry, the process of spore-forma- 

 tion begins. The plasmodium comes to rest, and it either forms a 

 single sporangium or divides into several portions, each of which 

 forms a sporangium. The external wall hardens to form the wall of 

 the sporangium, and the internal protoplasm breaks up into cells 

 surrounding each of the nuclei. Each of these cells in turn forms a 

 thick cell-wall and becomes a spore. 



Among creatures so simple it is plain that the difficulty of 

 establishing systematic criteria must be great. Indeed, in many 

 respects the classification of them in the absence of an extended 

 physiological examination of their habits and properties, their 

 response to the stimulations of different media, and the results of 

 such investigations as have been made upon bacteria, must remain 

 rather an empirical index serving for their identification than a classi- 

 fication in the modern scientific sense. With such necessary limita- 

 tions, Mr. Lister's system is very good ; and all biologists who take an 

 interest in this group must remain indebted to him for the beautiful 

 series of figures, which illustrate with great clearness the characteristic 

 forms of the sporangia and of the plasmodia in each of the species. 



Mr. Lister follows earlier authorities in separating the small 

 group of Mycetozoa in which the spores are not formed inside 

 sporangia from the great majority of forms in which sporangia are 

 formed. We think, however, that he uses the word sporophore 

 unfortunately in his synopsis. The relation between the spores and 

 the sporophore in the Exosporeae is not different in nature from the 

 relation between the spores and the stalk of the sporangium in those 

 Endosporeae in which the sporangium is carried upon a stalk. Indeed, 

 the stalk is most usually called a sporophore ; the point of difference 

 to be insisted upon is, of course, the existence or non-existence of 

 the sporangium, not the relation of the spores to the sporophore. 



