of Edinburgh , Session 1885-86. 
921 
forms, we find the primitive expression and fundamental secret of 
that difference which afterwards comes to saturate the whole body, 
and to effect what we know as sexual dimorphism. Without enter- 
ing into detailed illustration, it will be instructive to select the 
case of Yolvox. In this colonial organism, which is best regarded 
as a multicellular protist, the component cells are at first all 
alike/ They are united by protoplasmic bridges, and simply form 
a vegetative colony. In favourable environmental conditions this 
state of affairs may persist, or be interrupted only by partheno- 
genetic multiplication. When nutrition is checked, however, 
sexual reproduction makes its appearance, and that in a manner 
which illustrates most instructively the differentiation of the two 
sets of elements. Some of the cells are seen differentiating at the 
expense of others, accumulating capital from their neighbours ; and 
if their area of exploitation be sufficiently large, emphatically anabolic 
cells or ova result ; while, if their area is reduced by the presence of 
numerous competitors struggling to become ova, the result is the 
formation of smaller, more katabolic, and ultimately male cells. In 
some species distinct colonies may, in the same way, become pre- 
dominantly anabolic or katabolic, and be distinguishable as com- 
pletely female or male colonies. Again we reach the conclusion 
of a predominant anabolism effecting the differentiation of female 
elements, and of katabolism as characteristic of the male. 
(2) Another illustration may be selected. In the cells of a develop- 
ing anther an enormous number of crystals may be often observed 
to occur. Crystals are, however, usually regarded as accumulations 
of waste products. These anther crystals are, in fact, comparable 
to urinary deposits. Such accumulations do not, however, occur 
in the embryo-sac or in the female organs in spite of the homology 
in male and female development. They occur as signs of kata- 
bolism where we would naturally expect them — in the tissue of the 
male organs. 
(3) Or, again, in the structure of Chara or Nitella, there is, as 
is well known, an alternation between nodal and internodal cells. 
The internodal cells are actively vegetative, and go on increasing in 
size ; they do not divide, and may be justly regarded as emphatically 
anabolic. The nodal cells, on the other hand, are much smaller, 
and do divide. They are to be regarded as relatively more katabolic. 
