GENUS CERCOMONAS. 259 



The Cercomonas figured and described without a specific name by Messrs. 

 Dallinger and Drysdale in the 'Monthly Microscopical Journal' for August 1873 

 is here adopted as the type-form of the present genus, it so far, representing the 

 only species of whose distinct individuality, as derived from a knowledge of its 

 entire life-cycle, we can be absolutely certain. There can be but little doubt that 

 many of the species on which the title of Cercmnonas was first conferred by Dujardin 

 are transitional conditions of other genera, such as Monas, Oikomonas, Amphimonas, 

 and Heteromita, those only being consequently here retained whose characters accord 

 substantially with the foregoing diagnosis, and which have been described with suffi- 

 cient distinctness for future identification. In none of the forms yet known are any 

 details recorded respecting the manner in which food is ingested, but it may at the 

 same time be predicted that if a distinct mouth existed in the species so carefully 

 investigated by Messrs. Dallinger and Drysdale it would scarcely have escaped 

 attention. In one of the figures given by Stein of his Cercomonas longicauda, a green 

 vegetable corpuscle is represented as enclosed within the endoplasmic substance, 

 but no indication is given of any special inceptive area. The essentially free- 

 swimming habits of the type-form here described at once distinguishes it from the 

 somewhat similar tailed but adherent members of the genus Bodo. 



Cercomonas typicus, S. K. PL. XIV. FIGS. 22-30. 



Body ovate, rounded posteriorly, pointed and slightly curved anteriorly, 

 surface smooth ; flagellum long and slender, about twice the length of the 

 body ; posterior filament usually shorter than the flagellum. Length 

 1-3500". HAB. Fish macerations. 



This form is identical with the " Cercomonad " described by Messrs. Dallinger 

 and Drysdale in the above-named Journal. Its multiplication by the several 

 processes of coalescence, encystment, and resolution of the amalgamated zooids 

 into spores of infinitesimal minuteness, similar to those already described of Monas 

 Dallitigerii, was accurately determined. Rapid increase by the more simple 

 process of transverse fission was likewise abundantly observed ; the time occupied 

 by a zooid in thus dividing itself into two was ascertained in an average of forty 

 cases to be exactly four minutes and forty seconds. Adult individuals preparing 

 to conjugate or coalesce with one another assume the amcebiform condition repre- 

 sented at PI. XIV. Figs. 23 and 24; they then, with the aid of their extemporized 

 pseudopodia, creep about, retaining for a while their flagellate appendages, and 

 present under such conditions an aspect not unlike that of the Rhizo flagellate form 

 Mastigamatba simplex. Two of these amceboid zooids coming in contact fuse 

 intimately with one another, and losing their flagella become transformed into a 

 smooth, quiescent cyst, from which myriads of almost imperceptible spores are 

 subsequently liberated. 



Cercomonas longicauda, Duj. PL. XIV. FIGS. 17-20. 



Body elongate-ovate, fusiform, flexible, terminating posteriorly in a long, 

 undulating, tail-like filament, about twice the length of the body ; anterior 

 flagellum slender, usually shorter ; contractile vesicle single, laterally 

 located ; endoplast spherical, subcentral. Length of body 1-2700". 



HAB. Vegetable infusions. 



This species being figured with fuller details by Stein in the third volume of 

 his ' Infusionsthiere,' has permitted the addition of those data concerning the relative 

 positions of the endoplast and contractile vesicle which are wanting in Dujardin's 

 diagnosis. In one of the illustrations given by the first-named authority the animalcule 

 is represented in profile, and in a creeping state, presenting under such conditions a 



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