MORPHOLOGV OF THE CELL. 



an example, large cells, the oogonia (Fig. 2, /, Og), are formed in peculiar 

 receptacles; the space enclosed by the cell-wall is densely filled with fine-grained 

 protoplasm, which is at first homogeneous, but subsequendy breaks up into eight 

 portions (oospheres) ; these, completely filling up the cell-cavity of the oogonium, 

 press against one another and become polygonal. The wall of the oogonium 

 consists of two layers; the outer one splits, and the inner one protrudes in the 

 form of a sac, which becomes distended by absorpdon of water ; in this enlarged sac 



the oospheres become globular 

 (Fig. 2, //); when this bursts, 

 the oospheres, now completely 

 spherical, escape. By the fertilis- 

 ing action of other smaller proto- 

 plasm-masses, the antherozoids, 

 these balls of protoplasm or oo- 

 spheres are excited to further 

 development; on the exterior of 

 each fertilised oosphere or oospore 

 a colourless substance makes its 

 appearance, which hardens into 

 a continuous cell-wall. The newly- 

 formed cell now grows in two 

 different directions in different 

 modes, and produces, after further 

 transformations (Fig. 2, V and 

 IV\ a young Fucus-plant. 



Sdll more clearly does the inde- 

 pendence of the protoplasm of 

 a cell show itself in the formation 

 of the swarm-cells^ (zoogonidia) 

 of Algfe and of some Fungi. In 

 many cases, as in Stigeodonium 

 insigne (Fig. 3, B, a), the proto- 

 plasm of a cell filled with cell-sap 

 contracts, expels the cell-sap, and 

 forms a roundish ball, which, 

 escaping through an opening in 

 the cell-wall, swims about in the 

 water (C). While passing out, 

 the protoplasm shows, by its motions and changes of form, that it is soft and 

 extensible ; but, once freed, it assumes a definite form. ' Usually after some hours, 

 the swarm-cell comes to rest ; if killed by proper means, the protoplasm contracts 

 (JE, F, p), and a delicate cell-wall may now be recognised, which it did not 

 possess at the time of its exit, when it began to swim about. When once at 



FIG. 3. — Stigeoclotiiion insigne {^SXex Nageli, Pflanzenphysiol. Untersuch- 

 ungen, Heft \); A s. filament of the Alga consisting of one row of cells, with a 

 lateral branch ; f/ green protoplasm-masses (chlorophyll-bodies), imbedded in 

 the colourless protoplasm of each cell not shown in the drawing; B the proto- 

 plasm of the cells contracting and protruding through openings in the cell- 

 wall ; C swarm-cells still without cell-wall ; D one come to rest ; at E and F 

 killed ; the protoplasm /is contracted and shows the newly-formed cell-wall-;^ ; 

 Ha. young plant grown from the swarm-cell; G two cells of a filament in the 

 act of dividing ; the protoplasm of each cell {x, y) has split into two equal 

 parts, and contracted by addition of a reagent. 



^ [For the exact meaning of this term see Book II. Chap, i, the Introduction to Thallophytes, 

 The term 'swarming' is applied to any apparently spontaneous motion imparted to a naked 

 protoplasmic body by vibratile cilia.] 



