754 MUlilEL KOCEKTSON. 



as a o-eueral rule, extraordinarily free from bactei-ia, schizo- 

 mycetes, etc., and although a total of about 150 leeches were 

 examined, I never found them to contain any flagellates, or, 

 indeed, any protozoan parasites other than the hteraogregarine. 

 A large number of observations upon live material from the 

 leeches were made in the hope that the sequence of the 

 processes might be followed by direct observation, but this 

 proved to be impossible, as the development occurs in the 

 tissues of the leech. 



The blood upon being taken up l)y the leech is stored in 

 the large crop, where the blood-corpuscles undergo a gradual 

 degeneration. The blood passes in small quantities into the 

 intestine, where it is digested and absorbed. Blood-corpuscles 

 are never fonnd, nor even their nuclei, in a recognisable state 

 in the intestine, and this holds good even in the case of a 

 newly fed leech. A large number of live observations were 

 made, but no motile hi^mogregarines were ever found in the 

 crop. This particular htemogregarine appears to be digested 

 out of the corpuscle (Hgs. 25 and 26), and only to become 

 motile when it passes into the intestine. I am persuaded 

 that this cannot be universal amongst haemogregarines ; so 

 many species react almost instantly to the mere shedding of 

 the blood that I expect in other cases the parasites will be 

 found to become motile at once upon being taken into the 

 intermediate host. Motile haemogregarines are to be found 

 in tlie intestine at intervals all through the digestion, but 

 except in cases where the blood is very rich in parasites, 

 there are never a very large number present at one time. 

 The hasmogregarine never makes any attempt to attack the 

 wall of the crop. 



A number of hajmogregarines seem to degenerate in the 

 crop (fig. 27), but degeneration stages are only rarely found 

 in the intestine; it seems to fare with these, as with the 

 blood-corpuscles, that they disintegrate before reaching the 

 intestine. So far as my observation goes, neither the large 

 bean-shaped forms nor the completely recurved individuals 

 are to be recognised in the intestine. The individuals which 



