THE H^MOPLAGELLATES. 251 



after infection Leg'er observed, in the intestinal contents, 

 pyriform ookinetes without a flagellura ; some of these pos- 

 sessed a single large nucleus (i.e. a " compound " nucleus), 

 either at rest or in process of heteropolic division, Avhile 

 others had two nuclei, of which one was smaller than the other. 

 Four days later the intestine contained numerous Trypano- 

 somes which could be distinguished as belonging to one of 

 the three types described by Schaudinn in Trypano- 

 morpha, namely, indifferent, male and female. The indif- 

 ferent forms, it may be noted, multiply actively by longitudinal 

 fission (see p. 238). Other details of these various types 

 are given, but their further evolution and the manner of 

 their passage back into the loach was not followed. The 

 above-stated facts^ however, hardly leave room for doubt 

 that both these piscine Trypanosomes have a true, alter- 

 nating*, Hirudinean host. 



Billet's work (3) on Trypanosoma inopinatum is also 

 very important, and goes far towards proving both pi'oposi- 

 tions for this form. The author brings forward evidence to 

 show that (1) the alternate. Invertebrate host of this para- 

 site is another leech, Helobdella algira, and (2) that it 

 has an actual ontogenetic relationship with a Drepanidium 

 or Lankesterella parasitic in the same Vertebrate, and 

 which is, most probably, its Htemosporidian phase. The 

 investigation was somewhat complicated by the presence in 

 the same frogs of the common T. rotatorium, bvit, on the 

 other hand, the coincidence was instructive, since the result 

 obtained tends to show that that pai'ticular leech is not the 

 alternate host of the latter parasite. 



The principal facts brought out by Billet's experiments are as follows : — 

 (a) After the examination of a number of leeches which had been ectopara- 

 sitic upon frogs containing in their blood either Lankesterella (Drepa- 

 nidium) plus T. inopinatum plus T. rotatorium, or only Lankes- 

 terella, it was found that, in either case, the Helobdellre contained in 

 their intestine only T. inopinatum. Neither Lankesterella, as such, 

 nor T. rotatorium was met with in this host, (b) Moreover, Billet 

 several times observed in the intestine of the leeches, within twenty-four 

 hours after the time of infection, parasites which were more or less rounded 



