656 Fritsck.—Two Fungi , parasitic 
in Fig. 3. This moniliform shape of the parasitic hypha 
is due to the same cause as in R. nodosa , Dangeard ; that 
is to say, the Fungus expands considerably within each cell of 
the Alga, narrowing down each time it has to penetrate one 
of the transverse walls of the latter. The Fungus itself at 
this stage either presents no partition-walls whatever, or they 
only occur at very rare intervals ; this is readily discerned 
with a high power of the microscope. As the parasite grows 
on in front, it generally dies off behind, and* the posterior 
portion is then cut off from the living anterior part by the 
successive formation of transverse walls ; these generally arise 
at the points where the constrictions occur (Figs. 8, 10). 
The living portion of the Fungus has perfectly homogeneous 
contents of an opaque white appearance, occasionally inter- 
rupted by small drops of oily matter of a highly refractive 
nature (Figs. 3, 7). Nuclei were not observed. The segments 
are most commonly ovate, but occasionally spherical. The 
Fungus only rarely pursues a straight course within the Alga ; 
generally it is more or less zigzag or spiral 1 . 
The Fungus has the same effect on the cell-contents of the 
Alga as the species first described ; in both cases no deforma- 
tion of the algal filaments, such as Dangeard describes as 
occasionally occurring in the Lyngbya attacked by R. nodosa 
(cp. Dangeard, ’ 90 , p. 96), was observed. Fig. 3 shows the 
protoplasmic contents of the algal cell contracted around 
the segments of the parasite, whilst Figs. 4, 7, 8, &c., show 
stages in which the Fungus alone remains within the sheath 
of the Tolypothrix. 
Usually only a single fungal hypha is to be seen in each 
algal filament ; in a very few cases branching was observed 
to take place, both branches continuing to live inside the host. 
On the other hand, external branches, i. e. branches which 
penetrate the sheath of the Alga and emerge into the surround- 
ing water, are very common. Figs. 3 and 4 show early stages 
in the development of such branches, whilst Figs. 5, 6 , and 7 
1 In passing from one homogonium of the Alga to another the hypha narrows 
down and presents no constrictions (Fig. 8) ; cp. also Dangeard, loc. cit., p. 97. 
