GENUS DEL TO MO N A S. 283 



Perty detected on one occasion the presence of a posterior thread-like filament, 

 and upon which slender evidence only the species is here provisionally retained in 

 the genus Amphimonas. 



GENUS III. DELTOMONAS, S. K. 

 (Greek A ; monas.) 



Animalcules variable in form, subtriangular or wedge-shaped, attached 

 by an attenuate prolongation of the posterior extremity of the body, which 

 does not, however, assume the character of a distinct pedicle or caudal 

 filament ; flagella two in number, of equal length ; no distinct oral aperture. 

 Inhabiting fresh water. 



The animalcules of this genus, while corresponding with those of Amphimonas 

 in their fixed habits, and in the possession of two subequal anterior flagella, are to 

 be distinguished from them by their direct mode of attachment, without the inter- 

 medium of a specially differentiated pedicle. 



Deltomonas cyclopum, S. K. PL. XIV. FIGS. 60-65. 



Body exceedingly plastic and variable in shape, most usually elongate- 

 clavate, triangular, or wedge-shaped, somewhat compressed, widest and 

 truncate anteriorly, tapering gradually towards the attached posterior 

 extremity ; flagella similar in size and character, equalling the body in 

 length, springing from the lateral angles of the truncate anterior border ; 

 parenchyma colourless, granular ; contractile vesicle conspicuous, situated 

 a little in advance of the centre of the body; endoplast spherical, subcentral. 

 Length of extended body 1-3000". 



HAB. Pond water. Multiplying mostly by longitudinal, rarely by 

 transverse fission, and by the breaking-up of the body-mass into spores. 



This Flagellate type was found in the month of January 1877, literally encrusting 

 with its multitudes the carapace and limbs of specimens of a species of Cyclops taken 

 from a horsepond in the neighbourhood of Ashby-de-la-Zouch. The various contours 

 presented by different animalcules of the same colony are almost too numerous for 

 description. Simply ovate, clavate, symmetrically or obliquely pyriform, are among 

 a few of the leading variations from the typical triangular shape exhibited, these 

 variations depending more or less on the state of development or extension of the 

 individual zooids, as also upon the aspect in which they are presented to the view 

 of the observer. The species increases rapidly by longitudinal fission, the first 

 indication given of this process being the appearance of two flagella in place of one 

 only at each of the anterior angles (see PI. XIV. Fig. 63), this being speedily 

 followed by the gradual cleavage through the centre, from above downwards, of the 

 entire body-substance. The two zooids produced by this process of multiplication, 

 although usually completely separated, remain near to one another on the same 

 fulcrum of support, and in this way a single individual speedily produces an extensive 

 and closely aggregated colony. Not unfrequently instances have been met with in 

 which the units produced in this manner were collected in little clusters of four or 

 more individuals, the bases of which, if not organically united, sprang apparently 

 from the same point of attachment, as shown at Fig. 62. On more rare occasions 

 the phenomenon of transverse fission was likewise witnessed, the divided anterior 

 portion swimming off as a Heteromitous biflagellate monad destined either to lay the 

 foundation of a new community in a more remote district, or not improbably to aid 



