5 



FIRST GROUP. THALLOPHYTES. 



as the outer wall is free from them, the outside of the sphere appears clear and 

 transparent (Fig. 35, A] ; folds of the cell-wall run from the circumference to the 

 centre of each shield, and give it the appearance of being lobed in a radiate manner. 

 A cylindrical cell projects inward from the centre of the inner wall of each shield 

 almost as far as to the centre of the hollow sphere ; this is termed the handle or 

 manubrium. The flask-shaped cell (pedicel- cell) that bears the antheridium also 

 intrudes into it, thrusting itself between the four lower shields. At the central extremity 

 of each of the eight manubria is a roundish, hyaline cell, the head-cell (capitulum) ; 

 the frame-work of the antheridium is thus composed of twenty-five cells. Each head- 

 cell is surmounted by six smaller cells (secondary head-cells], and from each of 

 these proceed four long whip-like filaments, the numerous coils of which fill the interior 



FIG. 37. Nitella flexilis. A fertile branch of 

 natural size ; i internode ; b leaves. B upper part of a 

 fertile leaf b with the node A", and on it two lateral 

 leaflets nb and two very young oogonia S\ a the 

 antheridium. C older leaf with two leaflets ; a. mature 

 antheridium a, and two immature oogonia 5. />a half- 

 mature oogonium highly magnified. 



FIG. 36. Nitellaflexilis. A a nearly ripe antheridium at the end of the primary leaf, beside it two lateral leaflets ; / neutral zones ; 

 arrows show the direction of the ' streaming ' of the protoplasm. B a manubrium with its head-cell and the whip-like filaments, in 

 which the spermatozoids are formed. C extremity of a young filament. D middle portion of an older one. E one still older. 

 F mature antheridial filament with spermatozoids G. CG magn. 550 times. 



of the antheridium (Fig. 36, B]. Each of these filaments about 200 altogether is a row 

 of small disc-shaped cells (Z>, E, F\ the number of which amounts to 100-200. In 

 each of these 20,000-40,000 cells a spermatozoid is formed, a thin, spirally twisted 

 thread, thicker at its hinder extremity, and with two long delicate cilia at the other and 

 pointed extremity (Fig. 36, G). When the antheridium is ripe the eight shields 

 separate by the lessening of their spherical curvature, the spermatozoids escape from 

 their mother-cells and move about in the water ; the antheridia appear to break up 

 usually in the morning, and the spermatozoids continue in movement for some hours, 

 sometimes till the evening. 



