GENUS OIKOMONAS. 251 



This species has been obtained abundantly in a maceration of hay in spring 

 water, in which at times it absolutely swarmed. The relationship of the elongate 

 free-swimming zooids to the sedentary ovate or subspheroidal ones, was not 

 for a long while determined, the former being indeed chronicled in the author's 

 note-book as elongate nomadic monads, most nearly resembling the Monas 

 constricta of Dujardin, and representing probably an early and monoflagellate 

 condition only of the species described later on under the name of Sterromonas 

 formicina. The identity of the two was demonstrated while examining a group of 

 stalked individuals that had become isolated within a small space in the glass slide, 

 through the gradual evaporation of the water. As this space became still more 

 limited by the encroachment of air the animalcules apparently took alarm. Detach- 

 ing themselves, the pedicle contracted and disappeared within the posterior 

 protoplasmic substance, the body became at once less broadly ovate, and assumed 

 within a few seconds the elongate contour, with a slightly constricted central region 

 identical with the free-swimming types before observed. In this elongate form the 

 monads swam round and round the confines of the liquid space, now less than 

 the diameter of the field of the T Vinch objective, vainly seeking a pathway for 

 escape, and were ultimately dried up. This identity of the locomotive and fixed 

 forms being once discovered, the further verification of the fact proved a com- 

 paratively easy task, the transformation being observed not only of the fixed to the 

 free-swimming type, but that also of the latter to the sedentary one. In this 

 instance the animalcule became attached by an irregularly-shaped mucilaginous 

 extension of the posterior extremity, which gradually assumed a slender and thread- 

 like aspect accompanied by a shortening and thickening of the outline of the body. 

 The rigid extension of the flagellum in both the attached and motile phases of 

 this species imparts to it, in the latter instance, a stiffness of motion in the water, 

 corresponding closely with that of Sterromonas, with which it was at first supposed 

 to be identical. This apparent stiffness is shown by the application of reagents, 

 or when the animalcules become exhausted through the want of oxygen, to be a 

 mere optical aspect, the rotation of the distal end of the flagellum being then 

 conspicuous, while the whole organ as death approaches loses its seeming rigidity, 

 and becoming flexible, feebly undulates throughout its length. Reproduction by 

 the longitudinal fission of detached ovate examples of this species, accompanied 

 by a division of the conspicuous spherical endoplast, has been noticed, as also the 

 encystment and the breaking up of the encysted zooids into spore-like bodies. 

 Young individuals of elongate, conical outline, with a truncate anterior end and 

 rigidly projecting flagellum, which exhibited a similar stiff comportment during 

 natation, occurred abundantly among the adult animalcules. The smaller of these 

 immature forms measured about one quarter only of the length of the full-grown 

 specimens, every gradation in size from the one to the other being traceable. The 

 ingestion of food during the sedentary condition at different points of the periphery 

 was frequently observed. 



Oikomonas termo, J.-Clk. sp. PL. XIII. Fi -s. 78-80. 



Body ovate or subspherical, somewhat compressed, rounded posteriorly, 

 free-swimming, or attached by a thread-like pedicle of variable length ; the 

 anterior margin notched or emarginate and exhibiting a projecting lip-like 

 angle ; flagellum springing from the notch produced by the lip-like promi- 

 nence extended rigidly in advance and slightly curved, about twice the 

 length of the body ; parenchyma colourless, more or less granular ; con- 

 tractile vesicle posteriorly located ; endoplast spherical, subcentral. Length 

 of body 1-5000" to 1-3000". HAB. Fresh water and vegetable infusions. 



This species, regarded by Professor H. James-Clark (/. c. p. 306) as probably 

 identical with the Monas termo of Miiller and Ehrenberg, is referred by O. Biitschli 



