E. Hindlb 
473 
a fowl. With the first stage nymphs obtained from these larvae another 
fowl has also been infected and we are rearing these nymphs in order to 
see whether the infection is transmitted to their offspring, as in the 
case of 0. moubata. 
The study of the coccoid bodies in the developing eggs is of great 
interest for these forms seem to concentrate into particular regions of 
the embryo. The cells of the Malpighian tubule when in the embryo 
often contain enormous masses of the coccoid bodies, which, in some 
cases, are so numerous as to completely fill the cells. In this respect 
they agree with the similar stages of S. duttoni occurring in the 
developing eggs of 0. moubata (Leishman, 1910). If the developing 
eggs were kept at a temperature of 37° C. either long fusiform bacilli 
or spirochaetes were obtained, according to the time at which one 
commenced the incubation. 
If the eggs were placed in the incubator as soon as they had been 
laid the larvae did not hatch out until the 7th or 8th day and in the 
films made from them the simple elongation of the coccoid bodies into 
intracellular, long fusiform bacilli was observed (Fig. 5). No spiro¬ 
chaetes were found in the films made from the freshly hatched larvae, 
nor, in fact, from those made from the larvae after they had been kept 
in the incubator for another three or four days. Moreover, in these larvae 
the coccoid bodies and fusiform bacilli seemed to disappear after the 
7th day. 
On the other hand two batches of infected eggs that were allowed 
to develop at 28° C. for about a week before being placed in the incubator, 
both showed abundant spirochaetes in the larvae that hatched from 
them about four days later. In this case the various stages in the 
development of the coccoid forms into normal spirochaetes were the 
same as those occurring in the incubated adult tick. 
It seems possible, from a consideration of the above-described 
results, that whilst the coccoid forms are intracellular they can either 
multiply by transverse fission or .simply elongate into fusiform bacilli or 
short spirilla, identical in appearance with ordinary bacteria. In order 
to develop into spirochaetes it is necessary for them to escape from the 
cell into a fluid medium ; in the case of the tick, either the coelomic 
fluid, or the contents of the gut. When the eggs are allowed to 
develop at 28° C. for a few days before being placed in the 
incubator, the developing spirochaetes are able to escape from the 
cells into the coelomic fluid, which is not formed until late in the 
development of the larvae. As a result, in this fluid medium they 
Parasitology iv 
31 
