684 OEDER: DIPLOMONADIDA 



blepharoplasts to the posterior end of the body, including in its course the 

 nucleus, associated with which is a parabasal body. The Hypermastigida 

 are subdivided into a number of families and genera, including the Tricho- 

 nymphidse, Leidy, 1877, which have since been studied by Grassi (1917), 

 Kofoid and Swezy (1919), Koidzumi (1921), and others (Fig. 286). 



3. Order : CYSTOFLAGELLATA Haeckel, 1873. 

 This order includes certain marine Protozoa, of which Noctiluca miliaris, 

 a phosphorescence-producing organism, is the best known. The body is 

 spherical, and may reach a diameter of over 1,000 microns. It has a 

 groove leading to the cytostome, in front of which is a thick tentacle, 

 with a length equal to half the diameter of the body, and a single 

 fiagellum. Reproduction is by binary fission or bud formation. 



B. Diplozoic Forms. 



4. Order : DIPLOMONADIDA. 

 The flagellates belonging to this order ( = Diplozoa Hartmann and 

 Chagas, 1910) differ from all others in that the nucleus and other organs 

 are duplicated, so that the body has a bilateral symmetry. They may 

 be supposed to have originated from certain uninucleate Protomonadida, 

 which have commenced a division process that has been arrested before 

 division of the body has taken place. The order contains the three genera : 

 Hexamita, Giardia, and Trepo^nonas. 



Genus: Hexamita Dujardin, 1841. 

 The flagellates of this genus have pear-shaped bodies provided with 

 six anteriorly directed flagella, and two which arise from the posterior end. 

 There are two nuclei at the anterior end of the body. The genus was 

 founded by Dujardin (1841) to include three species, two of which occurred 

 in stagnant water and one in the intestine and pectoral cavity of frogs and 

 newts. He described the organisms as having pear-shaped bodies with 

 four anterior and two posterior flagella, hence the name Hexamita. It 

 appears that H. inflata of stagnant water is the type species of this genus, 

 though Dujardin placed in the same genus, H. intestinalis, the parasitic 

 form (Fig. 287). It is now known that the latter, as pointed out by 

 Grassi (1879) for the form in the frog, in addition to the two posterior 

 flagella, has six anterior ones, so that Dujardin evidently overlooked two 

 of the latter. Dobell (1909) points out that there is little doubt that 

 Dujardin was observing the eight-flagellate parasite, only six of the flagella 

 of which he was able to count. If he made this error over the intestinal 

 form, it is evident he was equally liable to make the same mistake as regards 

 the type species, H. inflata, of stagnant water, for he places them in the 



