These parasites are grouped with the haemoflagellates and occur in their vertebrate hosts exclusively as small, oval, cockle-shell-shaped bodies, measuring 2.5 × 3.0 microns. The protoplasm stains a faint blue and contains a rather large trophonucleus which is peripherally placed and gives the appearance of the hinge of the cockle shell. Besides this macronucleus we have a second chromatin-staining body which is often rod-shaped and set at a tangent to the larger nuclear structure. It is called the blepharoplast or micronucleus and stains a more intense reddish than the rather fainter stained pinkish macronucleus. One or more vacuoles are common in the cytoplasm. Some consider these nonflagellated bodies, which are usually found packed in endothelial cells of spleen, liver, lymphatic glands and bone marrow, as resting stages, the flagellate existence occurring in some other host than its vertebrate one. Patton has carried on an immense amount of experimental work with the bedbug and has noted the development of flagellate forms from the 5th to the 8th days in bugs which fed on kala-azar patients showing leishman bodies in their peripheral circulation. If the bugs are allowed a second feeding after the infecting blood meal the flagellates disappear within twelve hours, so that for full development in the bedbug a single feeding is requisite. He states that the flagellate forms change to post-flagellate ones by the twelfth day. At the same time, although much evidence exists in favor of the bedbug as host for the flagellate forms, it has not been shown experimentally that the bedbug is definitely connected with the transmission of the disease. Donovan is disposed to incriminate _Conorhinus rubrifasciatus_ as the transmitting agent and furthermore he feels that there has not been sufficient investigation of mosquitoes along this line. _Canine Leishmaniasis._—In the regions where leishmaniasis of infants occurs there is also found a similar disease of dogs and Basile has claimed that the disease is transmitted from dog to dog by the dog flea. As the dog has been regarded by some as the reservoir of the virus, so naturally the transmission of the disease from dog to child through the flea has been considered. Wenyon, however, tried to infect two young dogs with great number of fleas which had previously fed on dogs infected with canine leishmaniasis and at autopsy, five or six weeks later, was unable to find parasites in smears from spleen, liver or bone marrow and did not succeed in obtaining cultures from this material inoculated into tubes of N. N. N. medium.