17.] CHAPTER II. SPECIAL MORPHOLOGY OF THE MEMBERS. 81 



defined, ciliated, somewhat pear-shaped masses of protoplasm 

 destitute of a cell-wall (e.g. Botiydium, Ulothrix, Ectocarpus, etc.), 

 and are distinguished as planogametes. When, however, they are 

 not free-swimming (as in the Conjugate Algae) they have no defined 

 form nor are they ciliated. 



The gametes of heterogamous plants. The male gamete, when the 

 conditions are such that it must of necessity be free-swimming, is 

 generally a well-defined ciliated mass of protoplasm, termed a 

 spermatozoid: spermatozoids occur in the heterogamous Green and 

 Brown Algas (e.g. Yaucheria, Volvox, Sphseroplea, (Edogonium, 

 Chara, Fucus), in the Bryophyta, and in the Pteridophyta. In the 

 lower forms the spermatozoid is more or less rounded or pear- 

 shaped, somewhat resembling a planogamete of the isogamous 

 forms: but in the higher it is club-shaped or filamentous, thicker 

 at the posterior end, pointed at the anterior end where the two 

 or more cilia are borne, and more or less spirally coiled. 



An exception to this form of free male gamete is afforded by 

 the lied Algse, where the gametes are small rounded or oval bodies 

 destitute of cilia, and are distinguished as spermatia when first set 

 free they have no cell- wall, but they develope one before they come 

 into contact with the female organ. Very similar to these are the 

 spermatia of certain Ascomycetous Fungi, which have, however, a 

 cell- wall from the very first ; but there is some doubt as to the 

 sexual nature of these cells. 



When, owing to the proximity of the male and female organs at 

 the time of fertilisation, the male gamete has no considerable dis- 

 tance to traverse (e.g. Peronosporaceaa, Phanerogams), it is not 

 differentiated as a spermatozoid, but it is simply an amorphous cell 

 without a cell- wall. 



The female gamete, or oosphere, is not ciliated, nor is it, as a rule, 

 set free, but remains in the female organ until after fertilisation : 

 but in Fucus and its allies, the oosphere is extruded from the fe- 

 male organ before fertilisation. It is, generally speaking, spheri- 

 cal in form, as its name denotes. 



The gametes are developed from one or more mother-cells in 

 the gametangium. In isogamous plants, as a rule, each mother- 

 cell gives rise to more than one gamete, and commonly to a con- 

 siderable number (e.g. Botrydium, Ulothrix) ; but in Ectocarpus 

 and some other Phceosporece, each mother-cell produces but a 

 single gamete. Whilst in the higher heterogamous plants the 

 male gametes are each developed singly from a mother-cell, in the 



Y. s. B. o 



