
1905. | Life History of Trypanosoma balbianii. 373 
these, instead of dividing transversely to form two chromosomes, divide 
longitudinally, producing two longitudinal rows of dumb-bell shaped masses. 
Each of the masses now divides transversely, making a double row of 
chromosomes. The number of the chromosomes is now reduced to one-half, 
half the chromosomes of each longitudinal row being extruded at the centre 
of the dividing Trypanosome. The number of the chromosomes in the fully 
developed gamete appears to be 32. In its final form the male gamete is a 
much elongated mass of protoplasm containing 32 spherical masses of 
chromatin arranged at equal intervals along its length. The periplast is 
exceedingly thin. An undulating membrane may be, but more often is not, 
present. 
The gamete is very susceptible to external conditions, rapidly degenerating 
when these become unfavourable. 
Female Gamete.— Only two cases of the earlier stages of conjugation have 
been seen in stained preparations, and here the female gamete is seen to be 
similar to the male, only of greater thickness. 
Conjugation.—Conjugation appears to take place at the moment of the style’s 
dissolution, and to be of rare occurrence. In the two presumed cases of 
conjugation obtained, the male is seen to be lying in close apposition to the 
female for about one-sixth of its lenyth, the remainder of the two gametes 
being free from one another. Later stages, including the zygote, have unfortu- 
nately not been obtained. 
Encystment.—This has been observed to take place in culture and within the 
‘gut of the oyster. Encystment of the indifferent and female forms is to be 
distinguished, nuclear changes indicative of parthenogenesis taking place in 
the case of the latter. 
Encystment of Indifferent Forms—The forms about to undergo encystment 
cease to swim irregularly about, remain in one spot and enter upon a phase 
of activity, in which characteristic motions, varying considerably in different 
cases, are performed, a periodic reversal of direction being, however, common 
to all. During the motile period the nuclear band undergoes the series 
of changes described in the case of longitudinal division, condensing and 
breaking up into a number of isolated chromosomes. No differentiation out 
of the karyosom occurs.. Motion ceases and the periplast bursts, protoplasm 
and nuclear elements flowing out to form an irregular mass, which condenses 
to form a spherical cyst. The chromosomes undergo secondary fusion into 
irregular masses and later become indistinct. The periplast takes no part in 
the formation of the cyst. This method of encystment is reminiscent 
of the spore formation of the bacteria. The cysts do not appear to have a 
well developed membrane, although the contour is sharply defined. The 
