40 
Leueoeytozoon canis etc. 
already well advanced in development by the time the adult had 
hatched out from the pupa-like nymphal resting stage. Before the tick 
has fed the cysts are found lying in the lumen of the, as yet, narrow 
and empty diverticula, distending these much as a tennis ball might 
distend a stocking into which it had been pushed. But when the tick 
has attached itself and the diverticula become enormously swollen with 
blood, the cysts, which are still increasing in size, are pushed aside and 
come to lie in little pouches formed of the membranes of the gut wall: 
they then appear in dissection as if attached by a delicate pedicle to the 
outer wall of the gut. Large cysts lying outside the walls of the gut are 
therefore evidence of infection during the nymphal stage and have nothing 
to do witJi the development of vermicides taken in by the adult. In spite 
of this evident error of interpretation, however, the actual cycle 
described by Wenyon is correct and corresponds with that described by 
Miller (4) for H. perniciosum in the mite (Lelaps). 
The later stages of development are only seen in ticks which have 
been infected during the nymphal stages. During the stage of engorge¬ 
ment the large cysts develop rapidly and become fully mature and some 
may by rupture of the pouch in which they lie be set free in the body 
cavity of the tick. In a heavy infection these free cysts tend to collect 
together in the neighbourhood of the base of the rostrum, and some 
evidently are ruptured since the smaller sporocysts containing sporo¬ 
zoites are found free in the body juices. Since my original note was 
written I have examined numbers of very heavily infected ticks, some 
of them kept until they had become greatly shrivelled after oviposition, 
but I have never succeeded in finding sporozoites in the salivary glands 
or ovaries. 
In my first note( 2 ) I suggested that infection might occur by the dog 
swallowing the gorged adult tick and Miller has actually produced 
infection in this way with H. perniciosum by feeding white rats on 
infected mites. Unfortunately such an experiment has not yet been 
carried out in the case of L. canis. 
There is, however, another way in which infection may occur. In 
adults infected as nymphs I have on several occasions found numerous 
sporozoites within the gut. My work requires confirmation in this 
important point, but I have found them even when portions of the 
diverticula have been removed and washed, and when careful search 
with a lens showed that there were no adherent cysts. The presence 
of sporozoites in the lumen of the gut may be due to these having 
repenetrated the gut wall, or to cysts rupturing whilst still lying in 
