STUDIES ON AVIAN HiEMOPROTOZOA. 667 



endoplasm, running part of tlie way into the pleat of fold, 

 between the two (otherwise) closely apposed ectoplasmic 

 layers which constitute the membrane. The longitudinal 

 line about the middle of the fold is the edge or limit of this 

 inner endoplasmic layer. Laveran, in his account of T. 

 avium (6), calls attention to a " rib ^' or longitudinal 

 striation in the membrane. This striation corresponds, in all 

 probability, to the limit of an endoplasmic intrusion similar 

 to that just described. 



Apart from the undulating membrane, I have never seen 

 indications of an ectoplasmic layer. The trypanosomes I 

 have studied shoAv no sign of a well-developed, red-stain- 

 ing "periplast," such as has been described by several 

 workers in the case of T. lewisi, for example. As a matter 

 of fact, I should not expect to see any such appearance here, 

 since the ectoplasmic part of the folds of the membrane is 

 itself generally quite colourless, as already mentioned, and 

 at most shows in one or two instances the faintest possible 

 tinge of pink colour, which would be quite lost against the 

 stronger blue of the body. Nevertheless, there is no reason 

 to doubt that the parasites have a delicate ectoplasmic sheath, 

 investing the body generally. 



I will leave until later the consideration of the minute 

 structure of the trophonucleus. 



The above type of the parasite is the form which I have 

 found in the blood of the host — at any rate, in the chaf- 

 finches — during the winter and early spring months, when the 

 numerical factor is low, the infection being, as it were, per- 

 sistent, but in a quiescent and somewhat scanty condition. 



Young individuals, not yet full-grown, which belong to 

 this ordinary definitive type, can be readily recognised. 

 They are, of course, somewhat smaller, but their form and 

 general appearance agrees in most respects with that of the 

 adult parasites. The chief point of difference is that the 

 " snout " is usually not so elongated and drawn-out ; it is 

 more conical, but still sharply pointed (figs. 31-33). This 

 aflagellar part of the body attains the extreme degree of 



