136 Transactions of the Society. 



animal of the same kind which came under my notice contained the 

 same parasite. This is just to give yon some numerical idea of my 

 experiences. Some of these parasites are recorded and described 

 here for the first time, and it is this new work which is the main 

 excuse for this paper ; in many other cases the hosts are new, so 

 that 1 have tabulated the results for the sake of easy reference, and 

 I have printed those whicli are new or in new hosts in italics. I 

 have been very carefully through the literature, but with the con- 

 stant change of names on the part of the zoologists it is impossible 

 to be quite certain that I have not given myself too much credit. 



The organisms to which T am about to call your attention belong 

 to the two great grou])s of the Protozoa and the worms, those two 

 classes from which all the important endo-parasites are drawn. 

 They are all transferred from animal to animal by some blood- 

 sucking organism, such as a mosquito, a louse, tick, or leech ; and 

 it is known in a few cases, and surmised in the majority, that many 

 important stages in the life-cycle of the parasite take place in the 

 internal organs of these, their definitive hosts. 



I will (leal first with those parasites which live free in the serum 

 of the blood ; they are the Nematode worms, the trypanosomes and 

 other flagellates. 



First, the worms ; they all belong to the class of Filaria. Only 

 the embryos are found in the blood, as the adult filaria} could not 

 pass through the capillaries, and these micro-filariai do the least 

 harm to their host of any of the blood parasites. The severe effects 

 we know of filaria infection are caused by the adult worm, which 

 lives in the body and causes blocking of the lymph-vessels, ele- 

 phantiasis, etc. The wandering of the embryos into the ])eripheral 

 blood-vessels of the skin occurs i)eriodically at definite hours, and 

 is of course connected directly with the methods of infection. These 

 embryo tilarire are generally surrounded by a fine capsule which 

 they cast off when they enter the body of the mosquito, where their 

 further development takes place. 1 have found these filariie in the 

 blood of 15 nuimmals of l;> different species, 101 birds of 74 

 different species, and 13 re])tiles of 5 different species, and in 92 of 

 these species for. the first time. These filaria3 are new, at any rate 

 as regards their hosts, and have not been described before. 



Once again, with regard to names, it would of course be impos- 

 sible to give names to these from the embryos alone, and it is in 

 only about a quarter of the number of the animals that it has been 

 possible to find the ])arent worms. 



And generally in this paper I shall not attempt to give names 

 to any of the parasites described here for the first time. It is the 

 custom — and 1 think a very bad one — to name as separate any 

 similar parasite found in a new host ; it is quite ])ossible that we 

 are often dealing with the same organism, the host only being new, 



