ULOTHRIX AND HYDRODICTYON. 63 
theory of a reduction division of the chromosomes, which at the time 
received a wider acceptance than at present, 
In Hydrodictyon Klebs (’91) affirms that the process of cell-forma- 
tion, giving rise to gametes or asexual swarm-spores, occupies an 
intermediate position between simultaneous and successive cell-division. 
From what follows it will be seen that the process is a cleavage 
similar to that occurring in certain Phycomycetes, but, using the 
methods that he did, Klebs failed to perceive the true nature of the 
process. His account in substance is as follows: 
The first indication of cleavage is manifested in the appearance of 
numerous small clefts, pointed at the ends, in the plasma layer con- 
taining the chlorophyll (Fig. 18, A). This can be seen in material 
cultivated in darkness in a maltose solution, especially after the appli- 
cation of a weak plasmolysing agent. These clefts soon become 
longer and more numerous, neighboring ones thereby uniting with 
each other, so that finally the entire chlorophyll-bearing layer is seg- 
mented into pieces which are still connected, however, by fine plasmic 
threads. The cleavage is not confined solely to the chlorophyll- 
bearing layer, but extends into the colorless plasma in which the nuclei 
are situated. The plasma membrane and the wall of the vacuole are, 
on the contrary, unaffected. Previously to and during the cleavage 
the plasmic layer concerned frequently undergoes a contraction, thus 
giving rise to colorless spaces, so that this layer appears as a coarse 
net, as Pringsheim (71) has described for Bryopsis. These spaces 
contain also some plasma, and, as the plasma membrane and wall of 
the vacuole are continuous, the entire cell contents form still a unit, 
as shown by plasmolysis. The continuation of the cleavage results in 
the segmentation of the plasmic contents into numerous bands with 
irregular and sinuous contour (Fig. 18, B). These bands undergo 
still further segmentation (Fig. 18, C), until finally the plasmic con- 
tents are broken up into numerous small pieces, each containing a 
nucleus, which ultimately separate and develop into gametes (Fig. 18, 
D). The method of division in these portions referred to in Fig. 18, 
B, C (Klebs continues), appears to consist in a constriction, progress- 
ing from one side, but not entirely completed, since the individual 
parts remain in communication; yet direct observation shows also that, 
in the plane of division, a colorless line or furrow is frequently present, 
which gives the impression that the constriction may proceed from 
within. The same principle operating in the segmentation of the 
bands or pieces obtains also in the earlier cleavage of the whole 
plasmic layer of the cell. There is from beginning to end a progres- 
sive condensation, but the process that plays the chief réle is concealed 
from observation. 
