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salivary glands and ovaries : whether they actively seek out or are 

 attracted to these particular organs, or whether they 



penetrate all indiscriminately but can only survive Parasites in the 



. . , * Salivary Glands 



in these, is a question which does not appear to 



have attracted attention. 



The passage of a parasite from the gut to the salivary gland has not 

 been actually demonstrated, but it may be safely assumed that it takes 

 place by way of the haematocoele ; indeed, no other route is conceivable 

 in view of the anatomy of the parts. The length of time the parasite 

 remains free in the haematocoele, and the form which it assumes while 

 free, are questions to be decided in each case. In the case of the 

 parasites of malaria it is always assumed that the sporozoits are liberated 

 into the haematocoele of the host, a species of Anopheles, and find their 

 way into the salivary glands, penetrating through the basement mem- 

 brane, on the rupture of the oocyst; the exact route by which they reach 

 their destination is obscure. Presumably parasites reach the ovaries by 

 a similar route in the case of hereditary transmission. 



Another route from the gut to the salivary glands has recently been 

 suggested by Miss Robertson in the case of Trypanosoma gambiense in 

 Glossina palpalis. This observer states that, after a preliminary multi- 

 plication and differentiation in the gut, the trypanosomes pass forward to 

 the proventriculus ; there is some difficulty in reaching this situation, 

 however, and they only remain there so long as the fly is not subjected 

 to too long a fast. From the proventriculus they pass to the hypo- 

 pharynx, and up the duct to the glands. It is stated that the ' penetra- 

 ' tion of the trypanosomes into the salivary glands occurs quite clearly 

 ' from the hypopharynx, and the successive stages of the process can be 

 ' seen very well in the live state, in careful dissections at the appropriate 

 'period'; and further, that 'slender trypanosomes may in rare cases be 

 ' seen lying in small numbers, free in the hypopharynx of flies whose 

 ' salivary glands are not yet infected. They then come back along the 

 ' narrow duct of the salivary glands, and can be seen there as free-swim- 

 ' ming slender creatures '. 



With the protozoological aspect of the question we are not at present 

 concerned, but it is necessary to point out the anatomical difficulties 

 which lie in the way of such an explanation. In the first place, the 

 salivary apparatus of Glossina, as of all Diptera, is entirely separate from 

 the alimentary canal, the only point in common between the two being 

 that they open at the prestomum, that is, at the extreme tip of the pro- 

 boscis. Although the food channel in the proboscis and the salivary 

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