STUDIES ON AVIAN H.EMOPROTOZOA. 707 



fissiou is taking place, a small fusiform oi* pyriform individual 

 being cut, ((if from the large, more or less club-shaped parent- 

 form. Severa.l of Thomson's figures are, indeed, almost 

 identical with some of my figures. Another important point 

 is that distinctly trypaniform individuals were present, and 

 such forms were found to be more frequent later on, for 

 instance in a culture of tiie forty-second day. 



As Thomson says, it is probable that earlier phases in this 

 development might have been found before the seventh day. 

 It is interesting to note that Thomson figures an unaltered 

 trypanosome (as it left the blood of the fish) in the culture of 

 seven days. Thomson's view is that the large, club-shaped 

 trypanomonad individuals are derived directly from such 

 trypanosomes by an alteration of the body-form, most of the 

 protoplasm becoming concentrated in the aflagellar part of 

 the parasite, which thus becomes greatly swollen in appear- 

 ance. According to Thomson, there is no prior multiplication 

 of the parasite in an ordinary trypanomonad condition. 

 Hence in this case a type of form very similar to that which 

 I have found in my cultures (cf . figs. 97, 98) is attained by a 

 quite different process ; in the culture of the avian parasites, 

 the trypanosome-phase is quickly lost and active multiplica- 

 tion in the ordinary trypanomonad phase goes on. 



It is evident from this that the development of the piscine 

 type in cultures proceeds much slower than that of the Avian 

 form, and this bears out, in an interesting manner, the facts 

 so far known relative to the development of the two types in 

 the true invertebrate hosts (leech and insect) respectivelv. 



The Significance of these Cultural Forms of Try- 

 panosomes in Relation to the Question of an 

 Alternate Invertebrate Host. 



When we come to compare the chief types of form described 

 above as occurring in cultures of trypanosomes from different 

 vertebrates with the flagellates described by various authors 

 from blood-sucking invertebrates, which they have considered 



VOL. 55, PAKT 4. NEW SERIES. 47 



