36 Mr. E. A. Minchin. On the Occurrence of [Nov. 3, 



anything resembling a trypanosome. Finally the digestive tract was 

 examined, with the results stated. No trypanosomes were found in the 

 proventriculus. 



The films were made in the usual way by drying the smears, which were 

 then fixed with methyl alcohol and stained with Giemsa's stain. A few were 

 kept unfixed and have been fixed and stained for me recently by my assistant, 

 Dr. J. D. Thomson, with excellent results. It is a matter of great regret to 

 me now that none of my smears of this fly were fixed by the osmic-vapour 

 method. The method of drying smears is a drastic one, which is likely to 

 deform finer details, and in the present instance the cyst- wall is often injured, 

 being evidently of a soft consistence. 



The gut was divided into four regions and smears made from each. In the 

 anterior region of the intestine the ingested blood is of red colour, very 

 thick, and jelly-like and difficult to smear out nicely. Further back it gets 

 more fluid and begins to turn black. In the hinder part of the intestine the 

 blood is black and fluid. I refer to these three regions briefly as the red, 

 red-black, and black blood respectively. The black blood stops sharply and 

 suddenly at the point at which the Malpighian tubules enter the gut. The 

 proctodeum contains no blood, but only a yellowish fluid containing 

 innumerable coarse granules. 



I proceed now to describe briefly the process of encystation observed by 

 me in the fly. A glance at the preparation shows many different stages of the 

 process side by side. In the first place we find individuals in which encystment 

 has not begun (figs. 1, 2). These are forms for the most part very slender and 

 smaller than any of the forms of T. grayi found in the intestine of this or 

 other tsetse-flies ; but their most striking feature is the absence of any distinct 

 undulating membrane, so that they bear a great" resemblance to the genera 

 Herpetomonas and Crithidia, especially the latter. The flagellum is long and 

 appears to run down the side of the body. The blepharoplast has the large 

 size and rod-like form characteristic of T. grayi. The nucleus is either 

 compact or broken up into granules of chromatin. Division stages have been 

 found, but are very rare. 



In the first stages of encystment the flagellum becomes shortened and stains 

 more deeply, suggesting that as it diminishes in length it becomes thickened. 

 At the same time the cyst begins to appear as a layer of substance which 

 stains reddish with Giemsa, forming a cap at the hinder pole (figs. 3, 4). 

 These two processes continue until on the one hand the flagellum is com- 

 pletely retracted and on the other hand the body is enveloped in a pear- 

 shaped cyst, at first incomplete towards the pointed end (figs. 5, 6). The 

 flagellum appears to become retracted into a pink-staining vacuole (fig. 5, 



