468 University of California Publications in Zoology [Vol.20 



SUMMARY 



Menoidium incurvum is a small saprozoie euglenoid characterized 

 by a rigid body marked on the surface with from ten to fifteen widely 

 separated longitudinal striations; the body contains a number of 

 nearly colorless plastids, or paramylum bodies, located usually at 

 the anterior end, although occasionally at both ends. The gullet and 

 reservoir are similar in structure to those of other euglenoids, but 

 are not used for ingestion of solid food. 



The neuromotor apparatus is a simple system consisting of a 

 flagellum ending in a blepharoplast, from which a rhizoplast extends 

 to the nucleus. The granule, or eentrosome, at the base of the rhizo- 

 plast in Menoidium, and also in Euglena agilis, is similar to the extra- 

 nuclear eentrosome of such forms as Giardia and Trichomonas. Dur- 

 ing mitosis the daughter blepharoplasts remain connected for a time 

 by a paradesmose; this is similar in both Menoidium and Euglena 

 agilis to that of Trichomonas. There is some indication of a splitting 

 of the old flagellum instead of the expected outgrowth in mitosis, 

 but it is more probable that there is an outgrowth of the new flagellum 

 in close conjunction with the old. 



The resting nucleus contains an endosome surrounded by chro- 

 matin granules in the nodes of a linin network ; during mitosis these 

 granules become organized into distinct chromosomes, whose number 

 is tentatively determined to be twelve. The equatorial ring or plate 

 of the late metaphase is apparently produced by an unfolding of the 

 V-shaped chromosome pairs formed by the metaphase split; the free 

 ends of the V's migrate to opposite poles of the endosome, leaving 

 their other ends attached in the plane of the equator. At this stage 

 the chromosomes are parallel to the long axis of the endosome, and 

 they remain so until the late anaphase. Splitting of the chromosomes 

 occurs in the metaphase ; a precocious splitting in the preceding telo- 

 phase is possible, but there is no evidence whatever that this occurs. 

 The endosome contains no centriole at any stage of mitosis. The 

 nuclear membrane persists throughout nuclear division. 



Encysted forms of Menoidium have not been identified in either 

 living or stained material. 



