MORPHOLOGY OF THE CElt. 



falls into eight portions, and 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 pro- 

 trudes in the form of a sac, which distends by absorption of water ; in this 

 enlarged sac the portions of protoplasm become globular (Fig. 2, U); then this 

 also bursts, and the protoplasmic bodies, now completely spherical, escape. By the 

 fertilising action of other smaller protoplasmic structures, the spermatozoids, these 



spherical bodies are excited to 

 further development; out of the 

 interior of the ball of protoplasm 

 (the fertilised ovum) a colourless 

 substance next makes its appear- 

 ance, which hardens into a closed 

 cell-wall. The newly-formed cell 

 now grows in two different direc- 

 tions in different modes, and 

 produces after further transform- 

 ations (Fig. 2, Fand IV) a young 

 Fucus-plant. 



Still more clearly than in 

 these cases does the inde- 

 pendence of the protoplasmic 

 body of a cell show itself in 

 the formation of the swarm- 

 spores (zoospores) of Algae and 

 of several Fungi. Here in many 

 cases, as in Stigeodonium insigne 

 (Fig. 3 ; B, a), the protoplasm- 

 sac of a cell filled with cell-sap 

 contracts, lets the water of the 

 cell - sap pass out, and forms 

 a solid roundish lump, which, 

 escaping through an opening in 

 the cell-wall, and impelled by an 

 internal force, swims about in the 

 water (C). While it is passing 

 out of the cell-wall, the proto- 

 plasmic body shows, by its mo- 

 tions and changes of form, that 

 it is soft and extensible ; but, once freed, it assumes a definite specific form, con- 

 ditioned by an internal force. At last, usually after some hours, the swarm-spore 

 comes to rest; if killed by the proper means, the protoplasmic body contracts 

 {E, F, p), and a fine cell- wall may now be recognised, which it did not possess at 

 the time of its exit, and at the beginning of its swarming. When once at 

 rest, it also changes its form, and increases in volume, w^hile fluid cell- sap collects 

 in the interior. The cell formed in this way now grows in a manner dependent 



Fig. 3. — Stigeoclomunt tnsigne (after Nageli, Pflanzenphysiol. Untersuch- 

 ungen, Heft i) ; A a. branch of the Alga consisting of one row of cells, 

 with a lateral branch ; cl green-coloured protoplasmic structures (chlorophyll), 

 imbedded in the colourless sac of protoplasm of each cell not shown in the 

 drawing ; B the protoplasmic bodies of the cells contracting and protruding 

 through openings in the cell- wall ; C swarm-spores still without cell-wall ; 

 D one come to rest ; at E and F killed ; the protoplasm / contracts and 

 allows the newly-formed cell-wall h to be recognised ; H a young plant grown 

 from the swarmspore; G two cells of a filament in the act of dividing; the 

 protoplasmic body of each cell {.v, y) has temporarily split into two equal 

 parts, and contracted by addition of a re-agent. 



