438 MBE. G. BREBNER ON THE ORIGIN OF THE 
following is Fr. Schmitz’s summary of his results :—“ The thallus 
of the Florider, in general, is built up of a branched system 
of articulated filaments (Zellfdden). These filaments grow in 
length by the progressive acropetal division of the terminal cell, 
but transverse divisions do not occur in the articulations ( Glieder- 
zellen), nor longitudinal ones which are axially median.” The 
structure of the creeping thallus of D. filiformis, as described 
above, agrees very well with these views. 
Passing on to the consideration of the mode of origin of the 
ordinary Dumontia thallus, fig. 1 represents at a an early stage 
in the formation of the upright thallus. This more or less conical 
mass of filaments differs considerably in appearance from the 
surrounding tissue, chiefly owing to the individual members 
having a far greater number of transverse divisions than are 
found in the ordinary filaments of the creeping thallus. The 
appearances represented in this figure show the commoner mode 
of origin, which will be termed endogenous on account of the deep- 
seated position of the active filaments. 
In other cases the aggregations of very short-celled filaments 
are not infrequently found with their ends at the free surface: 
hence this may appropriately be termed the exogenous mode of 
origin (fig. 2, a). It is obvious that these specialized groups of 
filaments have arisen by the local transverse septation of the 
articulations. A careful study of the various stages shows that 
generally a few of the cells of a filament become transversely 
divided into two some distance from the upper end (fig. 4A, a’), 
or just at the top (fig. 2, x, and fig.3B), the terminal cell 
in the latter case likewise dividing. As a result, a more or less 
moniliform row is formed, which is seen fairly well in the filament x 
of fig. 2. ach of the short cells of the moniliform portion 
of the filament divides again (fig. 3 C, a’). Other divisions 
quickly follow until a part of the filament becomes converted 
into a considerable number, frequently twenty-four, of thin discoid 
cells (fig. 4B, a’). Comparison of a large number of groups in 
various stages of development leave but little doubt that these 
thin cells increase in number by the division of what may be 
called the apical cell of the specialized row. 
In the case of endogenous origin, which is most frequent, the 
filaments obviously must divide in an intercalary manner (i. e. 80 
that several articulations at the distal end take no part in the 
new formation), the outermost cell of those which do thus divide 
