126 
Theileria parva 
(4) Free parasites are rarely encountered in the blood. 
(5) Whilst the parasite is very pleomorphic, the commonest forms 
seen in stained preparations are ovoid or rounded and comma-shaped or 
clubbed. The proportion of bacilliform parasites is also fairly large and 
increases as the disease advances but may fall toward the end of the 
malady. Parasites having a pyriform shape are rare, and observations 
on living parasites indicate that they simply arise in the course of tran¬ 
sitory or amoeboid movements ; consequently such parasites are not to 
be compared with the common and typical pyriforms in Piroplasma , the 
latter, when formed, maintaining their shape for a considerable time. 
In other words, the pyriforms in Piroplasma represent a definite stage in 
the life history of the parasite, whereas in Theileria they do not. The 
study of stained and living Theileria confirms us in the opinion already 
expressed ( Parasitology , vol. n. p. 326) that this parasite deserves 
generic rank since it differs in essential characters from Piroplasma. 
(6) Judging from the study of stained specimens, the observer is 
tempted to conclude that the prevalent type of small ovoid parasite 
grows in size and becomes pleomorphic. The chromatin mass in ovoid 
parasites may become elongated or horse-shoe-shaped (figs. 9, 24, 36, 
42), and divides directly into two masses by a median constriction (figs. 
10, 12, 34, 35), the masses subsequently moving to opposite poles of the 
parasite (figs. 22, 32, 45). In bacilliform parasites the chromatin mass 
simply divides (figs. 19, 28, 30, 39) and the two masses wander to 
opposite poles of the parasite (figs. 27, 29, 30); in many cases the long 
parasite shows a marked bend at the point where the final division of 
the cytoplasm of the daughter cells is to follow (figs. 17—20, 30, 39, 44). 
Finally, in certain parasites which are rich in chromatin, the mass may 
undergo division into four giving rise to “ cross-forms ” (figs. 47, 48) the 
subsequent separation of the cytoplasm then liberating the daughter 
organisms (fig. 31). We have not observed more than eight parasites 
within an infected corpuscle. 
(7) Observations on living parasites ( Parasitology , vol. II. p. 335, 
Diagram 2) have established the fact that oval parasites may, when 
active, protrude processes, become constricted, or assume a pyriform 
shape. In some cases (vol. n. p. 336, Diagram 3, B and C) we observed 
the formation of bent dumb-bell-shaped parasites from ovoid or short 
rod-like forms. We were never able, however, to observe actual division 
in living parasites. Therefore we were led to doubt if multiplication of 
intracorpuscular parasites actually takes place (p. 334), and assumed that 
if it takes place the process “ must be very slow.” The careful study of 
