10 MAROUS M. HARTOG. 
Among the marine Siphonee, Dasycladus evinces a yet 
more subtle difference ; for Berthold has shown! that the 
gametes of one brood may refuse to pair, not only with one 
another, but also with gametes of certain other plants, while 
they do so with others; and yet he failed to make out any 
distinguishing character in the plants themselves.’ 
(2) AntsocAmy.—This is the second stage of karyogamy, 
where the gametes are similar in form, but of two sizes, large 
and small respectively ; and in their union a micro- always 
pairs with a mega-gamete. This may be regarded as the 
lowest form of sexual differentiation, the smaller more active 
microgamete being the male, the larger more passive mega- 
gamete the female. Exogamy is a necessity here, for each 
brood is all of one kind, large or small, as the case may be. 
If the gametogonia do not show a corresponding difference 
of size (which they do sometimes), the differentiation of the 
gametes is effected by the smaller number of bipartitions in 
the segmentation which produces the megagametes. Thus in 
Chlamydomonas pulvisculus the megagametes are pro- 
duced in twos or fours, the microgametes in eights. 
We shall note below the transitional conditions between 
isogamy and anisogamy presented by the genera Ulothrix 
and Pandorina. 
(3) Hypoocamy or HyrrranisocamMy.—This is our third stage, 
recognised but not named by previous writers. The gametes 
are similar, but differ not merely in size but in behaviour; 
for the megagamete absolutely goes to rest before the micro- 
gamete comes to unite with it. This process occurs in slightly 
different modes in two of the lower groups of Olive Seaweeds, 
Cutleriacee and Ectocarpex. The Ectocarpex are 
remarkable for the fact that their microgametes, as well as the 
megagametes, are facultative, or capable of independent 
1 * Botanische Zeitung,’ 1880, 648. Possibly the explanation is that the 
ultimate offspring belonging to the same cycle derived from a single zygote 
will not conjugate together any more than they will in certain Ciliate 
Infusorians; and that the individuals that showed this mutual sexual 
incapacity had this blood relationship, 
