Sexual organs 17 



Hydrodictyori). In the whole of the Conjugatae the gametangium 



gives origin to only one aplanogamete, but in other Algae it is 

 more usual for several gametes to arise from one gametangium. 

 Planogametes, such as are found in the Ulotrichaceae, are pear- 

 shaped bodies with the chromatophores more or less confined 

 towards the broader end, the narrower end being colourless. Two 

 cilia are inserted at or near the narrow, colourless end, and a red 

 pigment-spot is frequently present. They exhibit active move- 

 ments for a longer or shorter period of time and finally conjugate, 

 each pair coming into contact by their colourless poles. 



In those Alga? with dissimilar sexual cells the female organ 

 consists either of a single cell or a coenocyte known as the oogonium, 

 which is usually more or less spherical (e.g. CEdogoniacea?), some- 

 times attenuated into a beak (e.g. Vaucheria), or produced at the 

 apex into a long, narrow tube, the trichogyne (e.g. Coleochaetaceae). 

 An oogonium usually contains a single female cell or oosphere 

 (e.g. Vaucheriacere, GEdogoniaceae), but sometimes there are many 

 oospheres present (e.g. Sphseropleacea3). An oosphere is generally 

 a spherical cell containing chromatophores, and often with a clear, 

 colourless area at one side known as the receptive spot. It is at this 

 spot that the antherozoid enters during the process of fertilization. 

 In the Rhodophycea? the female organ is usually a inulticellular 

 structure (in the freshwater Red Alga? it is unicellular) termed a 

 procarp, which is divisible into two portions, a carpogonium and 

 a trichogyne. 



The male organ is known as the antheridium. It is usually 

 unicellular, but in (Edogonium it may consist of one or of many 

 cells. Each antheridial cell often gives rise to quite a number of 

 male cells (spermatozoids or antherozoids), but in the (Edogoniacese 

 it gives rise to two, and in the ColeochaetaceaB and most of the 

 Rhodophyceas to only one. Antherozoids frequently resemble the 

 asexual zoogonidia, but are usually smaller. They are commonly 

 pear-shaped, but may be elongate and almost rod-like. They 

 possess two cilia which are generally inserted at the pointed end, 

 but laterally in Volvox, Vaucheria, etc., and in (Edogonium theiv 

 is quite a tuft of cilia at the narrower end. They are as a rule 

 faintly coloured and often possess a red pigment-spot. 



Sexual organs have riot been observed in many of the Pro- 

 tococcoidea? and in the Syngeneticae, and are apparently entirely 

 absent from the whole class of the Myxophycea?. 



w. A. 2 



