GENUS TETRAMITUS. 313 



GENUS I. TETRAMITUS, Perty. 



Animalcules naked, free-swimming, plastic and changeable in form, 

 usually more or less conical and tapering posteriorly, with a truncate anterior 

 margin ; flagella four in number, inserted close to each other at some point 

 of the frontal border. No distinct oral aperture ; contractile vesicle and 

 endoplast conspicuous. HAB. Stale water and organic infusions. 



This genus was instituted by Perty, ' Kleinster Lebensformen,' 1852, for the 

 reception of two closely allied forms, Tetramitus restrains and T. descissus. By 

 several authors, including more notably Diesing and Biitschli, it has been assumed 

 that the genera Pyramimonas of Schmarda and Chlor aster of Ehrenberg, include 

 all the essential characteristics of the later one instituted by Perty, and which conse- 

 quently possesses no claim for recognition. A reference to Schmarda's original 

 figures and description of his type-form of the genus Pyramimonas, fortified by an 

 intimate acquaintance with a closely-allied species, has fully satisfied the author, 

 however, that the animalcules investigated and described by Perty represent an 

 entirely distinct generic form, his title being consequently retained in this treatise. 

 This decision, previously arrived at, has been entirely endorsed in Stein's recently 

 published volume, and in which, indeed, all three genera, Tetramitus, Chloraster, 

 and Pyramimonas, are admitted. 



Tetramitus restrains, Perty. PL. XIX. FIGS. 42-48. 



Body soft and plastic, subpyriform, compressed, tapering and attenuate 

 posteriorly, the frontal border abruptly truncate, with a small spout-like 

 projection at its lower angle ; a shallow groove extending from this point 

 towards the posterior extremity; flagella subequal, slender and flexible 

 throughout, exceeding the body in length, inserted into the small conical 

 projection of the truncate frontal border ; contractile vesicles two in number, 

 situated close to each other near the base of the flagella ; endoplast oval, 

 central. Length of body i-iooo" to 1-900". 



HAB. Standing water and animal macerations. 



This species, representing the Tetramitus rostratus of Perty and Fresenius, and 

 the Pyramimonas rostrata of Diesing, is beyond doubt identical with the so-called 

 " Calycine Monad," figured and described by Messrs. Dallinger and Drysdale 

 in the ' Monthly Microscopical Journal' for May 1871. Its life-history, as elicited 

 by the investigations of these authorities, coincides broadly with that of Heteromita 

 rostrata, described on a previous page. Multiplication by longitudinal fission, 

 accompanied by the temporary assumption of a softer semi-plastic state, repre- 

 sents the ordinary mode of increase, and has been already recorded by Perty. In 

 this process the subdivision of the cone bearing the four flagella takes its share, the 

 two newly developed zooids possessing at the time of separation only two flagellate 

 appendages ; these however subsequently divide rapidly in half, and thus secure to 

 the animalcule its full complement. The more important phenomena of increase, 

 through the genetic union of two animalcules followed by encystment and the break- 

 ing up of the amalgamated bodies into dust-like spores, was successfully traced through 

 its various phases. In a space of nine hours the minute dust-like spores attained 

 the characteristic aspect of the parent monads, and were simply slightly inferior to 

 them in size. The individual zooids preparatory to and during the act of coalescence 

 assume an altogether irregular and remarkable contour (see PI. XIX. Figs. 44 and 

 45). The anterior portion bearing the four vibratile flagella alone retains its original 

 outline, the whole posterior portion of the body protruding bluntly lobate pseudo- 



