HAZEN: NEW SPECIES OF LOBOMONAS 131 
its ancestry among those species of Chlamydomonas which posses 
walled gametes, and are therefore ranked as the primitive mem- 
bers of the genus, since their vegetative cells and gametes 
differ (visibly) only in point of size. Our two new species of 
Lobomonas, moreover, also resemble a number of the relatively 
primitive members of Chlamydomonas in their method of cell 
division, namely through a cleavage which is fundamentally 
longitudinal but early shifts to a transverse position. The 
question then arises, what influences led to the divergence of 
cell form, which is practically the sole basis of separation between 
the species forming the small genus Lobomonas and the much 
larger number comprised in Chlamydomonas. 
A CONSIDERATION OF MORPHOGENESIS IN PRIMITIVE ALGAE 
This whole problem of the origin and inheritance of cell 
form in primitive organisms is one of very great interest which 
has received comparatively little attention. Perhaps the most 
extended discussion of the question has been furnished by D’Arcy 
Thompson (22), who regards surface tension as the paramount 
factor in the determination of cell form. Though at one point 
he admits that ‘the physical cause of the localized inequalities 
of surface tension remains unknown’, and at other times hints 
that an internal chemical heterogeneity may have some influence 
in connection with such differences in surface tension, never- 
theless again and again he reiterates his main thesis in regard 
to unicellular organisms, ‘that not only their general config- 
uration but also their departures from symmetry may be correlated 
with the molecular forces manifested in their fluid or semi-fluid 
surfaces’. This explanation seems to us entirely inadequate 
and not in harmony with the general weight of evidence. For 
the particular organisms considered here and in the previous 
paper on Brachiomonas (6) we can offer little direct evidence; 
but there are certain facts which suggest that the conception of 
the non-homogeneity of the protoplasmic structure of the cell, 
as developed by Rhumbler (19) and Harper (12) supplies a 
much more workable hypothesis than the idea of mere surface 
tension forces. 
Passing over Rhumbler’s work on protozoa, the most 
thorough treatment of morphogenesis within a small group 
of primitive plants is found in the studies of Harper (11, 12) 
on Pediastrum. He believes that the general four-lobed form 
