West & West, — Observations on the Conjugatae. 45 
That it is not a perfectly normal condition is also proved 
by the numbers of failures where lateral conjugation was 
attempted h 
Against the sexuality of the Zygnemeae only two plausible 
objections can be raised ; these are the phenomena of lateral 
and cross-conjugation . It is clear that in the case of lateral 
conjugation sexual differentiation of the individual cells and 
not of the whole filaments must have taken place, and con- 
cerning this Bennett and Murray 2 state, ‘that there is some 
differentiation of this kind would appear from the fact that 
when lateral conjugation takes place in a group of four cells 
the zygospores are formed in the two centre cells, which 
may be regarded as female.’ This we find to be the case, 
as may be seen from the figures of 5 . Jurgensii and .S', inflata 
(Figs. 72 and 73). Under certain conditions why should not 
this individual differentiation take place ? Why should not the 
cells in a filament of Spirogyra or Zygnema be considered in 
a sense as only partially developed, further physiological 
changes taking place just antecedent to conjugation, which 
give the cells the characters either of a germ-cell or a sperm- 
cell ? We see no reason for regarding the filaments as sexual 
until conjugation is about to commence, and then instead of 
the reproductive cells being specially cut off (as in Temnoga - 
metum ), the contents of the individual cells undergo a profound 
physiological change, being imperceptibly converted into iso- 
gamous gametes. Also if the conditions of environment be 
such (as in an isolated filament) as to render it impossible for 
the whole of the cells of one filament to become of one sex, 
why should not individual sexuality of each cell be assumed ? 
In some cases scalariform and lateral conjugation occur in the 
same filament 3 , and within a few cells of each other. We have 
mentioned that a filament engaged in conjugation has the 
vigour of all its cells largely augmented, and may not the 
activity of the changes converting the ordinary vegetative 
1 West, Sulla Conj. delle Zygn., 1 . c., t. 12, f. 8. 
2 Bennett and Murray, Cryptogamic Botany, p. 267. 
3 Petit, Spirogyra des envir. de Paris (Paris, 1880), Plate I, f. 13. 
