W. S. Patton and C. Strickland 
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Crithidia- like or Herpetomonad form is exceedingly vague and abrupt, 
and it should be noted that no sexual cycle appears necessary in these 
trypanosomes. We are therefore unable to accept these authors’ results 
and consider all their experiments are contaminated with possible 
natural flagellates we have referred to above. 
In all the instances in which vertebrate trypanosomes have been 
described as undergoing developmental changes 1 in invertebrate hosts, 
the presence or otherwise of natural flagellates has been entirely 
overlooked, and the work that, is already recorded is of very little value. 
These natural flagellates are not “ cultural forms of trypanosomes” but 
are true parasites of invertebrates. They have been found in lice, 
fleas, mosquitoes, ticks, biting and non-biting flies, bugs and in leeches, and 
we now propose recording our observations on a flagellate one of us 
found in the alimentary tract of Gtenopthalmus agyrtes. This flea, 
the Hon. C. N. Rothschild informs Professor Nuttall, has not been 
previously recorded from the rat, Mus decumanus, but that it is very 
common on mice, moles and shrews. We took a large number, as 
many as 16 off one rat, from a batch of animals caught at a particular 
locality in Cambridge. A large percentage of the rats were infected 
with T. lewisi. 
Crithidia ctenopthalmi , n. sp. 
We have examined the alimentary tracts of 25 fleas, and found two of 
them infected with this parasite ; one of the fleas was from a rat 
infected with T. lewisi while the other flea came from a rat in whose 
blood we could not find any trypanosomes. The alimentary tracts of 
both the fleas, on being dissected out, were examined in the fresh 
condition ; the midgut of the first contained fresh blood but no parasites 
could be seen moving in any part of it. The whole alimentary tract 
was ruptured and the contents smeared out and stained with Giemsa’s 
stain ; a number of adult flagellates and encysting forms were found in 
it. The midgut of the other flea contained digested blood alone, no 
parasites were seen in it but, on carefully examining the contents of the 
rectum, motile flagellates as well as round motionless forms were readily 
seen. The rectum was isolated and its contents smeared out and 
stained with Giemsa J s stain. In this preparation it was possible to 
study the post-flagellate stage of this Crithidia. One of us (1908) has 
1 We do not deny the possibility of trypanosomes undergoing simple multiplication by 
longitudinal division; Minchin (1908) has clearly demonstrated this in the case of 
T. gambiense in G. palpalis. 
