GENUS OIKOMONAS. 253 



posterior extremity of the body close to its juncture with the pedicle, and falling 

 to the ground, formed around the base of this structure a small heap, which at the 

 end of half an hour the little monad still continuing to incept fresh particles 

 had accumulated to dimensions equal to and in some cases larger than its own 

 body. The possession by this species of a definite excretory area, not sufficiently 

 limited to be called an aperture, was thus demonstrated, and is of interest, with 

 relation to the somewhat similar but more highly complex excretory phenomena 

 exhibited by the compound type Anthophysa vegetans hereafter described. 



Oikomonas Steinii, S. K. sp. PL. XIII. FIGS. 65-70. 



Body in its motile condition very variable, spheroidal, ovate or elongate, 

 in the sedentary state more or less regularly pyriform and attached by the 

 tapering posterior extremity, which is not sufficiently prolonged as to con- 

 stitute a distinct pedicle ; flagellum undulating, not extended rigidly or in 

 an arcuate form, equalling the body in length ; contractile vesicle single, 

 subcentral, endoplast posteriorly located. Length 1-1500". 



HAB. Vegetable infusions. 



The above title is here proposed for the form figured by Stein in his recently 

 published volume under the name of Cercomonas termo, and presumed to be identical 

 with the Monas termo of Muller and Ehrenberg. It being, however, entirely 

 separate from the type previously connected with that title by Professor Clark, 

 it becomes incumbent to introduce a new one for its distinction. Whether or not 

 the present form or Professor Clark's species represents precisely the animalcule 

 upon which Muller and Ehrenberg conferred the particular title of Monas termo, it 

 is next to impossible to determine, there being, in addition to these, a whole host of 

 monadiform beings that present, under a similar comparatively low magnifying power, 

 an aspect identical with that reported by the earlier authorities of the type in ques- 

 tion. The new species next described, exhibits, in both habits and external form, 

 broad general features that, without the employment of a high objective, entirely 

 coincide with those of the present species, and is, therefore, quite as probably 

 identical with the Miillerian or Ehrenbergian type. 



Oikomonas Steinii is, according to Stein's illustrations here reproduced, 

 eminently social, assembling in clusters upon the surface of the Bacteria-films or 

 vegetable debris contained in the infusions that give it birth. One of the alto- 

 gether irregular contours that may be assumed at will by the adult zooids of this 

 species is represented at PI. XIII. Fig. 67. In their younger and more minute 

 condition they present, as shown at Figs. 69 and 70, a much more regular ovate 

 contour, the posterior extremity being sometimes acutely pointed. Stein's proposed 

 reference of this type to the genus Cercomonas is, however, by no means justified, no 

 structure taking the form of a permanent tail-like appendage being exhibited in 

 any of his accompanying figures. 



Oikomonas rostratum, S. K. PL. XIII. FIGS. 73-77. 



Body evenly ovate or pyriform in its free-swimming condition ; gibbously 

 ovate with a wider central region in the attached state, the anterior ex- 

 tremity usually rostrate and curved ventrally, the posterior one attached 

 immediately to the object of support, or so attenuated as to form a more 

 or less distinct pedicle, this pedicle never exceeding and rarely equalling 

 the entire length of the animalcule's body ; flagellum extended obliquely 

 and rigidly from the curved anterior end, equalling the body in length; 



