462 Keene. — Cytological Studies of the 
Vuillemin (33) and Dangeard (9) have offered evidence as to the 
nature of the fusion of the contiguous walls of the gametangia. It will 
suffice here to say that the two walls coalesce, forming a single separating 
partition between the two branches. Previous to the cutting off of the 
gametes from the suspensors, large vacuoles are formed a short distance 
back in the swellings. The formation of these vacuoles usually takes place 
before the resorption of the separating wall. These vacuoles enlarge, 
becoming wedge-shaped. On their inner margins, a narrow isthmus of 
protoplasm is left connecting the protoplasm of the suspensors with that 
of the gametangia. Towards the margin of the gametangium, however, 
the point of the wedge-shaped vacuole cuts through the protoplasm, forming 
a cleavage furrow that extends to the wall of the gametangium (PI. XXXV, 
Fig. 4). In some cases, the cleavage furrow appears to be cut in without the 
aid of the vacuoles. The line of cleavage remains distinct, and very soon a new 
wall is built in from the outer wall of the gametangium (PI. XXXV, Fig. 5 ). 
Dangeard has suggested that this wall is in the form of a diaphragm which 
gradually closes in, but he offers no evidence to support his view. The 
relation of this diaphragm is very evident in the present preparations. As 
the wall is built in, the circular opening is gradually closed, like a diaphragm 
coming clear together, and cutting through the narrow isthmus of protoplasm. 
When the wall closes, the cellulose-like material continues to pile up for 
a short time, forming a papilla-like projection which the remaining strands of 
protoplasm also tend to draw out. This is the ‘ canal ’ described by Leger. 
Vuillemin has failed to recognize this structure in his study of the membrane 
of the zygospore. In PI. XXXV, Fig. 5 , the inner edge of the wall is 
shown as it cuts into the protoplasm at this point. The vacuoles and nuclei 
are somewhat elongated in the plane parallel to the long axis of the isthmus. 
The final cleavage is caused, either by the closing of the diaphragm, or by 
a furrow which precedes the new membrane so closely as to be indis- 
tinguishable. Thus it can be seen that this little structure that has 
received the passing attention of many, and had various functions allotted 
to it, is an unimportant result of the delimiting of the gametangium. 
In no cases have the orifices described by Dangeard and Leger been 
observed. 
As soon as the wall which separates the gametes from the suspensors 
is complete, and in numerous instances at the formation of the large 
vacuoles, the wall separating the gametangia is dissolved from the centre 
outwards. As has been said, the contents of one gametangium usually 
completely fill its cavity, while in the other there may be, and usually is, 
a marked retraction of the protoplasmic mass. When the separating wall 
is resorbed, there is a marked activity on the part of that portion of the 
mass that has extended clear to the wall, while the protoplasm of the other 
gametangium shows a further retraction before the influx of the active 
