12 



MORPHOLOGY OF THE CELL. 



This form of free cell -formation is distinguished from the preceding by the circum- 

 stance that the whole protoplasm (and not a part only) collects round several centres. 

 If the whole proto[)lasm, in its contraction, were to form only one mass, which some- 

 times happens, the case would be analogous to Rejuvenescence. 



There occurs also in Achlya a variation of this process, when it forms its swarm-cells 

 or zoogonidia (Fig. 9). The protoplasm in the club-shaped swollen end of a hypha 

 [contains a number of small nuclei which multiply by bipartition] ; it breaks up 

 into a large number of small portions {A), [each including a nucleus,] which become 

 completely rounded off {a) after their escape from the cell in which they are produced 



Fig. 8.— Oogonia and antheridia of Achlya lignicola, growing on f^lG. 9.— Cell in which are produced the 



wood in water; the course of developtnent is indicated by the letters v^—/^. swarm-cells or zoogonidia of an Achlya. 



a the antheridium, b its tube penetrating into the oogonium (x 550). (X 5So). A one still closed, B one allowing 



the zoogonidia to escape ; beneath it a 

 'ateral shoot c ; a the zoogonidia just es- 

 caped ; b the abandoned membranes of the 

 zoogonidia which have already swarmed ; 

 e swarming zoogonidia. 



(B), and then clothe themselves with a delicate membrane, which they abandon {b) 

 when their movement commences {e). 



4. Formation of Reproductive Cells by Division of the Mother- Cell. — In 

 the protoplasm of a cell new nuclei are formed by division; round each of these a 

 portion of the protoplasm collects and becomes rounded off with a greater or less 

 amount of contraction, in order to form a new cell ; in this manner the entire proto- 

 plasm of the mother-cell is completely used up ; its cell-wall alone remains, if it possess 

 one, which is not always the case. 



The formation of the spores of Mosses and Vascular Cryptogams, and of the pollen- 

 grains of Phanerogams, ahvays takes place by the division of the mother-cell into four 



