114 C(. CLIFFORD DOBELL. 
anterior ends come in contact and fuse. One flagellum is 
lost. By means of the remaining one the conjugants swim 
about during conjugation. Hach nucleus divides once and 
one of the daughter-nuclei at once degenerates (f). A second 
nuclear reduction occurs in which a chromatin granule (or 
granules?) is extruded (g). This process might also be de- 
scribed as a heteropole division. ‘Two courses are now open 
to the partially fused monads containing two reduced nuclei: 
(1) The nuclei may fuse (7) and the cell undergo a process 
of remodelling, whereby a zygote monad—aindistinguishable 
from an ordinary individual—is formed (a) ; the zygote may 
then continue to divide (a—d), and subsequently its descen- © 
dants may encyst (k). (2) Or the flagellum is drawn in, the 
zygote rounds itself off (7), and a cyst is formed. This is at 
first soft and gelatinous, but subsequently becomes hardened 
and more or less encrusted. The nuclei fuse inside the 
cyst. In whichever way the cysts have been formed they 
are apparently identical in appearance and subsequent history. 
They are capable of being dried up, and when they reach a 
suitable medium once more (i.e. the feeces of the frog) they 
liberate a small hyaline monad (1) which grows up and 
repeats the cycle of events just described. 
The gametes are not differentiated from the ordinary indi- 
viduals—i.e. every individual appears to be a potential 
gamete—and no sexual differences exist between the two 
members of a pair of conjugants. It may be noted, however, 
that one conjugant appears to absorb the other after it has 
lost its flagellum. 
The cysts are swallowed by frogs and toads, and reach the 
rectum by way of the digestive tract. Asa rule the cysts do 
not set free their contents until the faeces have left the frog. 
But sometimes the monads emerge from their cysts and lead 
a semi-parasitic life in the large intestine. Development does 
not appear ever to be completed inside the frog. 7 
