THE H^EMOFLAGELLATES AND ALLIED FORMS 313 



which it takes up in vertebrate blood, and that in this way stages 

 of the life-cycle of two or more distinct parasites may be confused 

 together. Up to the present, however, no blood-sucking insect has 

 been proved satisfactorily to harbour flagellate parasites not derived 

 from vertebrate blood. 



After deducting doubtful species of Crithidia, there remains a 

 residue which appears to comprise genuine, independent species, 

 parasites of the digestive tract of insects. As examples of such 

 species may be cited C. campanulata, recorded from the digestive 

 tract of Chironomus plumosus (Leger, A.P.K., ii. 1903, p. 180), 

 from that of the larva of Ptychoptera (Leger and Duboscq) and 

 of caddis-worms (Mackinnon, 547) ; O. gerridis, from Gerris spp. 

 (Patton, 550 ; Porter, 555) ; and possibly others. The life-cycle 

 of C. gerridis has been investigated by Patton and Porter. The 

 parasite appears under two principal phases : an active, flagellate 

 phase, which grows to a large size, and multiplies by fission, 

 sometimes very actively, forming rosettes ; and a resting, non- 

 flagellate Leishmania - form. The flagellate forms may be free 

 in the digestive tract, or may attach themselves to the lining 

 epithelium of the gut by their flagella. The non- flagellate forms 

 are found in the crop, where they grow into the adult phase, 

 and in the rectum, where they become encysted. The flagellate 

 phase is found throughout the digestive tract and in the ovaries, 

 but has not been observed to pass into the ova The encysted 

 forms pass out of the rectum, and infect new hosts by the 

 contaminative method. 



IV. THE GENUS LEPTOMONAS (HERPETOMONAS). 



The genus Leptomonas comprises typical intestinal parasites 

 of insects, especially Diptera and, above all, Muscidce. Several 

 species are also known in Hemiptera. They are in most cases 

 parasites of the insect alone, having no alternate host, and infection 

 is brought about by the contaminative method, so far as is known, 

 cysts dropped by one host being accidentally devoured by another. 

 But some species are found as parasites of the latex of Euphor- 

 biacese, and in this case an alternation of hosts occurs. The para- 

 sites are taken up from the plants by bugs (Hemiptera) which 

 suck their juices, and by the agency of the bugs the flagellates 

 are inoculated into other plants again (Lafont ; Bouet and Roubaud, 

 530 ; Frana, 537, 538). There can be little doubt that in this case 

 the bug is the primary, the plant the secondary host. The plants, 

 or the parts of them that are infected by the Leptomonas, suffer 

 considerablv. The term ' flagellosis ' has been proposed for the 

 disease. 



