C. Basile 
measure up to 26p, x 5/x. The appearance of these large forms is evidently 
due to the artificial conditions prevailing in the culture, and, since many of 
them show vacuolated plasma, they may well represent degenerative forms. 
In addition, elongated and spherical forms of rather large size and with 
granules scattered in the plasma are to be noted. These forms have been re¬ 
garded as sexual forms; or (Rogers, Marzinowski) as conjugation forms. I 
have made repeated and prolonged observations in this regard, using a 
thermostat at 22° C., but I have never observed conjugation to take place. 
The morphological study of cultural Leishmania both of infantile and 
canine origin has been carefully followed by Visentini at the Lister Institute. 
I shall refer to the principal deductions of this writer, dealing chiefly with the 
morphological identity between the evolutive forms of Leishmania in fleas 
and the forms encountered in cultures. 
( c ) Leishmania in the transmitting host (Ctenocephalus canis, Pulex irritans). 
Patton, describing the life cycle of the flagellate Protozoa of insects (Herpe- 
tomonas and Crithidia ), has distinguished three stages—the pre-flagellate, the 
flagellate, and the post-flagellate. These stages are also to be noted in the 
cycle of Leishmania in fleas. The pre-flagellate stage is found in the flea’s mid¬ 
gut; the flagellate stage in the hind-gut; and the post-flagellate stage in the 
rectum and faeces; these three stages correspond morphologically to those of 
Leishmania in cultures. 
In the flea’s mid-gut, the parasites show the same characteristics which 
they present in the peripheral blood and in the haematopoietic organs of in¬ 
fected vertebrates; when fixed and coloured they appear rounded, oval, or 
pear-shaped (Plate XXI, figs. 16-19), they measure on an average 2-4 p in 
diameter. The protoplasm assumes a delicate pale blue tint; the nucleus of a 
reddish violet colour is almost always compact, sometimes granular; the 
blepharoplast is sometimes absent, as has been noted in parasites from the 
haematopoietic organs; when it is present it may be rounded or rod-shaped 
and of the same, or a deeper tint than the nucleus. 
Leishmania in this pre-flagellate stage divides longitudinally; first the 
nuclei and then the plasma. In this manner forms are produced indistinguish¬ 
able morphologically from those in the haematopoietic organs (Plate XXI, 
figs. 20, 21, 22). 
In some stained preparations however, I have seen certain parasites (Plate 
XXI, fig. 23), which show two nuclei and a blepharoplast. I have carried out 
numerous experiments to ascertain whether these might represent sexual 
forms, but with no success. 
In fleas experimentally infected and kept at a temperature of 22° C., after 
36 hours from infection I have observed flagellated forms in the intestine, 
these are morphologically identical with the pear-shaped or elongated cul¬ 
tural forms which have been already described. 
In fact, these flagellate, pear-shaped parasites in fleas have almost the 
same measurements and appearance as the cultural forn"° being 7-9/x in 
