S. R. Christophers 
39 
The error iu this step was not merely that of missing the large cysts 
since described by Wenyon. Just as I believe Wenyon has done, I here 
short circuited the developmental cycle by describing stages which 
were not the result of development of parasites taken in by the adult tick 
at all, but were the last stages of a development undergone by a previous 
brood of parasites taken in by the tick in its nymphal stage. 
To continue the story of development one may return to the large 
deeply staining irregular bodies which are the latest stage I have 
correctly described as following the ingestion by the adult tick of blood 
containing haemogregarines. After these bodies have grown somewhat 
in size, the nucleus exhibits karyokinetic changes and, strange as such 
a fact may seem, the oocyst (?) divides first into two and then into four. 
I have repeatedly confirmed the occurrence of this act of division, and 
the groups of two or four large deeply staining bodies the result of 
fission occur quite regularly and form a conspicuous feature in develop¬ 
ment at a certain stage. Later development consists in a great increase 
in size of these forms, which, however, as they increase in size begin to 
take the stain less and less deeply. The chromatin also which at first 
stains readily becomes in the later stages more difficult to stain until it 
is clear that one is dealing with a cyst wall. By the time these bodies 
have reached 40 ya or so in diameter they are demonstrably the early 
stages of the large cysts described by Wenyon and can readily be picked 
out under a low power. 
Wenyon’s account suggests that the large cysts found by him lying 
outside the gut wall were the result of development of parasites taken 
in when the adult tick had been fed. But in my own observations, 
when an adult tick was fed on blood containing haemogregarines, 
the.se required so long a period to develop that, even when the tick had 
shrivelled after the lengthy process of oviposition, the large cysts were 
only partially mature. In ticks kept for 24 days (in the Madras 
climate) most of the cysts were still immature and still later many had 
become stained with blood-derived pigment and were seemingly under¬ 
going degeneration. Also all the cysts thus foi’med lay loosely amongst 
the products oj digestion in the lumen of the gut. 
When a tick was fed as a nymph upon an infected dog the same 
sequence of developmental changes took placebut the large cysts were 
1 In my original description of the cycle I recorded two experiments in which parasites 
had disappeared by the fourth day from nymphs fed on infected blood. Later experiments 
have shown that, on the contrary, development proceeds very rapidly in the nymph. 
Possibly I was misled by this fact and overlooked the oocysts in my early experiments. 
