THE HAEMOFLAGELLATES 203 



of blood drives this mass before it, in the form of a rolled-up ball, until 

 it reaches the junction of the ileum and colon (Fig. 4, c), the narrowest 

 point of the intestine. The wall here is very thin and easily ruptured, 

 and most of the Trypanosomes pass through it, into the vascular lacunae 

 around, whence they are carried to the heart. Finally, the parasites 

 become arrested in the sinus surrounding the pumping-organ of the 

 pharynx, where they continue to multiply and collect again into 

 agglomerated masses, which press on the wall of the pharynx in this 

 region. By the end of the third digestive period, these clumps of 

 Trypanosomes have broken through, and partly block up the lumen ; 

 and in the next biting act they are forcibly ejected into the blood of the 

 owl. Thus the parasites cannot leave the gnat until the fourth meal, 

 including that which effected their entry, has taken place ; and Schaudinn 

 found that the shortest time elapsing between entrance and exit was seven 

 or eight days, when the insects were maintained at the optimum tempera- 

 ture for digestion. 



An interesting discovery is the occurrence of true hereditary infection. 

 After breaking through the wall of the colon, a few of the Trypanosomes, 

 usually females, instead of being carried forwards, may pass to the 

 ovarian follicles, penetrate into the young eggs, and so infect a succeeding 

 generation. 



According to Prowazek (I.e.), the behaviour of Trypanosoma 

 hwisi in Haematopmus and its passage through the louse resembles 

 in the main the account above summarised. Such differences as 

 there are stand in close relation, on the one hand, to the somewhat 

 different mode of feeding and of absorption of nutriment in the 

 louse, and on the other hand to the fact that T. hwisi appears to 

 be more resistant to " external " influences. 



With regard to other Mammalian Trypanosomes, the evidence 

 so far available is mostly to the effect that they are confined entirely 

 to the alimentary canal, and never occur in other organs of the 

 insect. Concerning T. gambiense in G. palpalis, Minchin, Gray, 

 and Tulloch (I.e.) remark that these parasites were found only in 

 the mid-gut, and never passed either backwards into the proctodaeum 

 or forwards into the proventriculus. 1 According to Stuhlmann (I.e.), 

 T. brucii is apparently much more at home in G. fusca (which may 

 prove to be its true specific host), being met with in different forms 

 from the hind-gut (colon) to the proboscis. But this author also 

 emphasises the fact that the Trypanosomes were never observed 

 anywhere else, and, particularly, never in the salivary glands. The 

 only positive observation of the occurrence of Trypanosomes in the 

 salivary glands which need be taken into account is the recent 

 statement made by Koch (29) that, of the different types which 



1 Gray and Tulloch (/.c.) stated that they had observed T. gambiense in the 

 salivary glands, but Minchin has since shown that what they took to be salivary 

 glands was in reality proventriculns ; moreover, they may have been dealing, not with 

 T. gambiense, but with one of the other parasites in this fly. 



