14 



suit of the spermatozoid coalescing with the egg-cell is, as in 

 the preceding case, the formation of a zygote, which generally 

 undergoes a period of rest before germination (the Florideae are 

 an exception, a fruit-body, cystocarp, being produced as the result 

 of coalescence). 



An example of fertilisation is afforded by the Alga, Spharoplea annulina (Fig. 

 10). The filamentous thallus is formed of cylindrical cells with many vacuoles (r 

 in A) ; some cells develope egg-cells (B), others spermatozoids ((7), the latter in 

 a particularly large number. The egg-cells are spherical, the spermatozoids of 

 a club- or elongated pear-shape with two cilia at the front end (G ; E is however 

 a swarmspore). The spermatozoids escape from their cells through apertures in 

 the wall (o in C) and enter through similar apertures (o in B) to the egg-cells. 

 The colourless front end of the spermatozoid is united at first with the "re- 

 ceptive spot" of the egg-cell (see F), and afterwards completely coalesces with 

 it. The result is the formation of a zygote with wart-like excrescences (D). 



The female (parthenogenesis) or male (androgenesis) sexual cell 

 may, sometimes without any preceding fertilisation, form a new 

 individual (e.g. Ulothrix zonata, Cylin drocapsa, etc.). 



Systematic division of the Algae. The Algae are divided 

 into the following ten classes : 



1. SYNGENETICLE ; 2. DINOFLAGELLATA, or PERIDINEA ; 3. DIATO- 

 MACE^l ; 4. SCHIZOPHYTA, FlSSION-ALGJ; ; 5. CONJUGATE; 6. CHLORO- 

 PHYCE^, GREEN- ALGJS; 7. CHARACEJ;, STONEWORTS; 8. PILEOPHYCEJ: ; 

 9. DlCTYOTALES; 10. RHODOPHYCE^. 



Among the lowest forms of the Algae, the Syngeneticae, the 

 Dinoflagellata, and the unicellular Volvocaceae (Chlamydomoneae), 

 distinct transitional forms are found approaching the animal 

 kingdom, which can be grouped as animals or plants according to 

 their method of taking food or other characteristics. Only an 

 artificial boundary can therefore be drawn between the animal 

 and vegetable kingdoms. In the following pages only those forms 

 which possess chromatophores, and have no mouth, will be con- 

 sidered as Algae. 



Class l. Syngeneticae. 



The individuals are uni- or multi-cellular, free-swimming or 

 motionless. The cells (which in the multicellular forms are loosely 

 connected together, often only by mucilaginous envelopes) are naked 

 or surrounded by a mucilaginous cell- wall, in which silica is never 

 embedded. They contain one cell-nucleus, one or more pulsating 



