C. M. Wbnyon 
329 
Further development of the leucocytic stage in the tick 
Rhipicephalas sanguineus. 
The development of this haemogregarine in the tick was first 
described by Christophers. The method of investigating the develop¬ 
ment adopted by him, viz. the making of smears of the contents of the 
ticks, was not the best for giving clear pictures of what was taking 
place. By making smears it is impossible to avoid breaking up the 
large oocysts and scattering the sporocysts. In this way Christophers 
appears to have described the sporocysts as oocysts. 
In the present instance the following method was adopted. Ticks 
were taken from infected dogs and the abdomens were opened by making 
a cut round the margin with fine scissors. By careful dissection with 
needles it was possible to remove the ventral chitinous plate intact, 
leaving all the organs behind. The organs were then removed in one 
piece and immediately fixed in Zenker’s fixative. These fixed organs 
were brought home for examination, Serial sections were cut and 
these stained with haematoxylin. In these sections it was possible to 
follow many of the stages of development of the haemogregarine. 
The first step in the development has been clearly described by 
Christophers and consists in the liberation of the cysts from the leucocyte 
and finally the escape of the haemogregarine from the cyst. The free 
haemogregarines can be found in numbers in the intestinal contents of 
the ticks. 
I have also been able to trace haemogregarines within the epithelial 
cells of the gut and also between the epithelial cells and the basement 
membrane. Finally they are to be found outside the basement mem¬ 
brane amongst the body contents, usually, however, close to some fold of 
the gut. 
Unfortunately, I have not yet been able to follow out the conjugation 
process. 
For haemogregarines this has been most clearly described by 
Reichenow for H. stepanowi. The haemogregarines taken into the gut 
of the leech associate in pairs, and still within the gut a process of 
conjugation takes place which is very similar to that of the coccidian 
Adelea ovata. In one of the haemogregarines the nucleus divides into 
several parts, and one of these parts unites with the entire nucleus of 
the other haemogregarine. The remainder of the divide nuclei are 
discarded. After this the ^zygote increases in size and breaks up into 
sporozoites which pass through the gut wall of the leech into the 
