CONJUGATE. 



inner surface and gradually forms a complete septum. The divid- 

 ing wall gradually splits, and the two individuals separate from 

 each other, each one having an old and a new half. The two 



FIG. 36. Cosmo rinm botrytis. A-D Different stages of cell-division. 



daughter-cells bulge out, receive a supply of contents from the 

 parent-cells, and gradually attain their mature size and develop- 

 ment (Fig. 36-B-D). Exceptions to this occur in some forms. 



CONJUGATION takes place in the simplest way in Mesotcenium, where 

 the two conjugating cells unite by a short tube (conjugation-canal), 

 which is not developed at any particular point. The aplanogametes 

 merge together after the dissolution of the dividing wall, like two 

 drops of water, almost without any trace of preceding contraction, 

 so that the cell-wall of the zygote generally lies in close contact 

 with the conjugating cells. The conjugating cells in the others 

 lie either transversely (e.g. Cosmarium, Fig. 37 d ; Staurastrum, 

 etc.), or parallel to one another (e.g. Penium, Closterium, etc.), and 



FIG. 37. Cosmarium menegliinii : a-c same individual seen from the side, from the end, 

 and from the edge ; d-f stages of conjugation ; g-i germination of the zygote. 



emit a short conjugation-canal (Fig. 37 d) from the centre of that 

 side of each cell which is turned towards the other one. These 

 canals touch, become spherical, and on the absorption of the divid- 

 ing wall the aplanogametes coalesce in the swollen conjugation- 

 canal (Fig. 37 c), which is often sin-rounded by a mucilaginous 

 envelope. The zygote, which is often spherical, is surrounded by 

 a thick cell-Avail, consisting of three layers ; the outermost of these 



