THE H^MOFLAGELLATES AND ALLIED FORMS 311 



dulating membrane only extends along two-thirds of the length of 

 the body, after which the posterior flagellum becomes free. The 

 kinetonucleus, situated at the extreme anterior end of the body, 

 is relatively very large, usually exceeding the trophonucleus in 

 size, and is sometimes constricted into two or three portions, but 

 is generally a compact mass which stains deeply in preparations. 

 In T. helicis, according to Jollos, it is prolonged backwards into 

 fibrils, usually two in number, which extend some way down the 

 body, and are probably comparable to an axostyle. The tropho- 

 nucleus has a vesicular structure with a conspicuous karyosome. Its 

 position in the body varies, being in some species close behind the 

 kinetonucleus, in others near the middle of the body. It often 

 appears to be lodged completely in the undulating membrane, which 

 in this genus is often very broad and less sharply defined than in a 

 trypanosome, appearing as the border of a flattened body. The 

 cytoplasm frequently contains numerous " chromatoid grains." 



Trypanoplasms in the blood of fishes often exhibit marked 

 polymorphism, with two extremes of size, small and large (Fig. 134, 

 B, C). According to Keysselitz (454), the large forms are the 

 gametes which conjugate in the leech, and are distinguishable as 

 male and female forms, but the statement requires confirmation. 

 From the investigations of Robertson (503) on the development, 

 it appears more probable that the large forms are simply full-grown 

 individuals, ripe for multiplication by fission. Unfortunately, 

 next to nothing is known of the reproduction of the parasites in 

 the vertebrate host, though it has been observed that their numbers 

 are subject to considerable fluctuations, and that a fish showing 

 at one time a very scanty infection, of the blood may have a 

 " relapse," and appear later well infected. Keysselitz accuses 

 these parasites of pathogenic properties, but this charge is founded 

 on observations on fish in captivity, in which weakened powers of 

 resistance may lead to abnormal activities on the part of the parasite 

 (compare also Neresheimer). 



The development of blood - trypanoplasms in the invertebrate 

 host, which is in all known cases some species of leech, appears to be 

 of a comparatively simple type as compared with that of trypano- 

 somes, and consists of little more than rapid multiplication by 

 binary fission to produce a swarm of relatively small trypano- 

 plasms, some of which, more slender and elongate in form, pass 

 forwards into the proboscis, and are inoculated by the leech into 

 a fish. Conspicuous in this development, as compared with that 

 of trypanosomes, is the entire absence of any uniflagellate forms, 

 crithidial or other. So long as a trypanoplasm is in an active state, 

 it is invariably biflagellate. Resting forms without a locomotor 

 apparatus may occur. In T. helicis, Friedrich describes winter 



