40 



PROTOPLASM 



Fig. 31. — Male sexual 

 cells (gametes or sper- 

 matozoids) of the liver- 

 wort Pallavicinia. 



are much alike throughout the Hving world, whether in a starfish, 

 a fern, or a mammal. They are relatively large, nonmotile, with 

 abundant protoplasm and considerable stored food (Fig. 30). 

 Male sexual cells are quite specialized. In lowly plants and in 



practically all Metazoa (multicellular ani- 

 mals), the sperm are small, active cells, with 

 very little protoplasm surrounding the 

 nucleus (Figs. 30, 31, 32). The cycads and 

 the closely related Gingko tree are the highest 

 members of the plant kingdom to possess 

 motile male cells. Most of the lower plants 

 (algae, mosses, ferns, etc.) have motile 

 (swimming) male sexual cells, but in higher 

 plants the male gamete, or sex cell, has lost 

 the property of motility and is carried by the pollen tube to the 

 egg in the base of the flower where fusion of the two sex nuclei 

 takes place. The fusion of the male nucleus with the female 

 nucleus constitutes fertilization. 



Unusual Primitive Organisms. — Certain lowly forms of living 

 matter consist of protoplasm with many nuclei, housed 

 in bodies of macroscopic size. Such multinucleate 

 bodies may be termed noncellular. They cannot be 

 regarded as single cells in the strict sense, for they 

 contain many nuclei ; nor are they tissue, for there are 

 no cross walls. They are cells in so far as they are 

 enclosed in one wall or membrane. The Plasmodium 

 (protoplasmic body) of the slime molds is a structure 

 of this kind (Fig. 1). The botanists claim the slime 

 molds as plants and call them Myxomycetes ("slime 

 fungi ") ; while the zoologists claim them as Mycetozoa 

 ("fungus animals"). The Plasmodium, or body, of 

 slime molds is a naked mass of protoplasm often attain- 

 ing an area equal to the size of one's hand but ex- ^^^ 32 _ 

 ceedingly thin. It is a primitive mass of almost wholly Sperm of the 

 undifferentiated protoplasm like an amoeba except for ^'^^^'^^"• 

 its many nuclei. One can imagine a thousand amoebae fusing to 

 form a single, multinuclear, undivided mass of protoplasm ; indeed, 

 in just such a way may the myxomycete Plasmodium actually 

 arise. The "amoebae" are called myxamoebae and are amoeba- 

 like, swimming spores which germinate from the spores of the 



