210 University of California PiMications in Zoology [Vol. 20 



except at mitosis, when they teud to destain. They are the most promi- 

 nent organelles in the living and in the stained cyst because of their 

 optical properties and stainability. 



The parabasal bodies tend to fade out at mitosis in the free flagel- 

 lates (pi. 24, figs. 7, 8, 11) and are found at the metaphase only with 

 the greatest difficulty, if at all, often only as vague clouds in heavily 

 destained slides. They are not homologues of the chromatoidal bodies 

 of intestinal amoebic cysts, but their enlargement during eneystment 

 and their dense stainability during mitosis in the cysts of Giardia 

 strongly suggest their functional analogy to the ephemeral chroma- 

 toidal bodies of the cysts of the intestinal amoebae. 



The homology of the parabasals of Giardia is indicated by their 

 shape which is that of a curved rod ; by their position with relation 

 to the posterolateral flagella, the homologues of the undulating mem- 

 brane of the triehomonads ; by their connections by a rhizoplast with 

 the blepharoplasts ; and by their behavior in mitosis. They are 

 homologous with the curved parabasal of Chilomastix (parabasal, 

 Kofoid and Swezy, 1920) alongside the cytostome with its undulating 

 membrane ; with the curved chromophile rod in the base of the un- 

 dulating membrane of Protrichomonas, Tritrichomonas, Trichomonas, 

 Pentatritrichomon-as and Trichomitus, which we have called (Kofoid 

 and Swez}^, 1915, 1920) the parabasal; and with the chromophile rod 

 coiled about the axostyle in Parajoenia (Janicki, 1911). There are 

 two of them present in Giardia because this genus is a bilateral, 

 binucleate organism derived from the triehomonads by duplication of 

 the nucleus and its attendant neuromotor system, including the para- 

 basal, and by a reversal of symmetry of the neuromotor system of one 

 of the two constituent cells. 



It is to be noted in this connection that the two parabasals lie 

 asymmetrically in the cytoplasm and that the sagittal plane which 

 parts them does not coincide in vertical position with that parting the 

 other organs. In other words, the morphological sagittal plane which 

 passes between the two parabasals is variously inclined in the dorsal 

 protoplasmic mass according to the varying positions of this pair of 

 organs. It is characteristic of the parabasal of some polymastigote 

 flagellates to vary considerably in its position, as for example, in 

 Parajoenia, although it is fairly constant in its relation to the un- 

 dulating membrane in the triehomonads. 



The parabasals of Giardia enterica present a great variety of 

 appearances according to their position and their relations to stages of 



