TRYPANOSOMA GAMBIENSE 537 



forms in increasing numbers. They are to be regarded as the regular 

 proventriculus type, and difier from the broad forms which they are 

 replacing in having a more finely granular cytoplasm, a nuclear karyosome 

 reduced in size, and a nuclear membrane which stains more deeply (Fig. 224, 

 12-13). Division of the slender forms may still take place. During this 

 multiplication period there are produced an enormous number of trypano- 

 somes, which invade the anterior part of the mid-gut, and finally the 

 anterior gut and proventriculus. The anterior part of the anterior gut 

 and the proventriculus contain the long slender trypanosomes which invade 

 this portion of the intestine between the tenth and twentieth day. Pro- 

 longed fasting causes the infection to pass back again till it becomes 

 limited to the middle and hind part of the mid-gut. A fresh feed again 

 brings the infection forwards to the proventriculus. If, however, new 

 blood is taken in while the proventriculus infection exists, the trypano- 

 somes maintain their position. The long slender trypanosomes are the 

 forms which were seen by Stuhlmann (1907) in the proventriculus. 



The further development is brought about by the slender proventriculus 

 forms passing into the labial cavity and hypopharynx, and thence into the 

 narrow tubular portion of the salivary gland, which consists of a narrow 

 tube, a broader cellular part, and finally the still broader terminal glandular 

 portion (Fig. 224, 14-16). The trypanosomes attach themselves to cells 

 of the cellular part or commencement of the glandular part. They 

 gradually transform into broad crithidia forms with rounded posterior 

 ends (Fig. 224, 16-20). They multiply, and gradually the cavity of the 

 gland becomes filled with flagellates which vary in shape and size 

 between tadpole-shaped crithidia forms and trypanosome forms resembling 

 very closely the vertebrate blood type (Fig. 224, 20-23). Division of all 

 these forms takes place, the crithidia forms being mostly attached to the 

 surface of the glandular cells. Fresh slender trypanosomes are constantly 

 travelling up the duct from the hypopharynx, so that there is a continuous 

 production of fresh crithidia forms, which in their turn produce the try- 

 panosomes of the blood type. The flies seem to become infective from 

 two to five days after the slender forms invade the gland. The whole 

 development occupies about twenty days. The cytology of the gland 

 forms calls for no special remarks except that their nuclei appear to be 

 richer in chromatin than those of the slender invading forms. 



It will thus be seen that there is an intestinal multiplication phase of the 

 trypanosome forms, leading to the formation of slender trypanosome 

 individuals which invade the proventriculus and hypopharynx. These 

 pass to the salivary glands by way of the duct, and become flagellates of 

 the crithidia type, which in turn gives rise to metacyclic trypanosomes, 

 closely resembling the blood type which commenced the developmental 



