Miss M. Robertson. Flagellate Infections in [Feb. 24, 



the coccidian cycle, but here again the condition is not without its reference 

 to the question of the phylogenetic development of parasitic protozoa. The 

 close relationship between the Hsemogregarinse and the Coccidia is now well 

 established, not to mention the general parallelism in all essential features 

 between the cycle of the malarial organism and that of any typical coccidian. 

 Not to lay undue weight on these points, the main feature here, as in the 

 previous instance, is the arrival of an intestinal parasite in the mouth-parts 

 of a sucking insect, which is, however, still a plant sucker. 



The concurrence of the flagellate and coccidian parasites in the Leptoglossus 

 and the fact that they have reached the salivary gland in both cases is rather 

 striking in view of the frequent association of flagellates and Haemogregarines 

 in the blood stream of vertebrates. 



Dysdercus casiatus (XIV), the red cotton-bug, shows an occasional infection 

 with a typical herpetomonas ; so far the parasites have only been found in the 

 gut. Only a small number of infected specimens have been examined, 

 figs. 8-10 show the general characters of the parasites ; no crithidial forms have 

 been found in these infections. 



Carbula jipcnsis (X). — This small bug shows rare and generally slight 

 infections with a herpetomonas. 



Two sets of infection (one in a reduviid XV, the other in a capsid bug V) 

 now come to be considered which differ from those hitherto handled in that 

 crithidial forms are present in large numbers as well as the typical " needle- 

 and-thread " herpetomonads and the broad forms from which they spring. 

 It is almost impossible to come to a really satisfactory decision as to whether 

 there are two different species present or whether all the forms represent 

 different stages of one species. I am inclined to consider, however, that in 

 each of the two cases one is dealing with a single parasite, and that the 

 crithidial forms, though sometimes present in large numbers, are more or less 

 transitory growth forms, and that the slender herpetomonads (11, 20, and 21) 

 are the adult individuals. Nevertheless the opposite view could be so well 

 defended and has so much in its favour that it must be considered as 

 practically an open question until more evidence is to hand. 



The facts that, in my opinion, weigh the scale in favour of one species in 

 which the long herpetomonads are the adults and the crithidia transitory 

 growth forms are as follows, and apply equally to either of the two sets of 

 infections : — 



1. The herpetomonad infections are sometimes found unaccompanied by the 

 crithidial forms, but the converse has never been observed. 



2. The crithidial forms are generally present in strong, actively multiplying 

 infections. 



