284 ORDER FLAGELLATA-PANTOSTOMATA. 



in compassing the still more rapid multiplication of the species by a genetic fusion 

 with another individual, followed by the breaking-up of the united zooids into spore- 

 like elements. That a sporular mode of increase does occur in connection with 

 this form, was fully demonstrated by the discovery occasionally, among the others, 

 of pyriform encysted individuals, in which the whole body-substance was divided 

 into minute oval bodies as shown at Figs. 64 and 65, such metamorphosed animal- 

 cules evidently representing the characteristic sporocyst stage recorded of numerous 

 other flagellate types described in this treatise. 



Fam. VIII. SPONGOMONADID^S, Stein. 



Animalcules symmetrically ovate ; usually social, invariably secreting 

 an external protective covering, which may take the form of horny loricae, 

 a gelatinous, more or less granular zoocytium, or an arborescent tubular 

 zoothecium ; flagella two in number, of equal length ; no distinct oral 

 aperture. Inhabiting fresh water. 



The representatives of this family group are to be distinguished from those 

 of the Dendromonadidae or Bikoecidae with which their supporting or protective 

 fabrics most nearly correspond by the symmetry of their bodies and the equal 

 development of the two flagella. The majority of forms included are remarkable 

 for the considerable and often visibly conspicuous size attained by their compound 

 colony-stocks. 



GENUS I. CLADOMONAS, Stein. 



Animalcules ovate, with two anteriorly inserted, equal-sized- flagella, 

 living in social colonies, dividing by longitudinal fission, and building up a 

 tubular and more or less regular, dichotomously branching zoothecium ; 

 the tubular branches not united to one another in a fasciculate manner, but 

 remaining distinct throughout their length, and enclosing each at its distal 

 end a single zooid ; the basal end of each tubule sometimes separated 

 from the preceding one by a distinct joint or dissepiment ; zooids possessing 

 no distinct oral aperture. Inhabiting fresh water. 



The independence or non-fasciculate arrangement of the tubular branches of 

 the zoothecium of this genus distinguishes it from that of Rhipidodcndron, next 

 described, with which it otherwise substantially corresponds. The form and struc- 

 ture of the enclosed animalcules are in both instances closely identical. 



Cladomonas fruticulosa, Stein. PL. XVIII. FIGS, n AND 12. 



Zoothecium arborescent, erect, branching in the same plane, the separate 

 ramifications short, rarely exceeding twice the length of the zooids, straight 

 or flexuose ; the bodies of the zooids evenly ovate, usually projecting for 

 about half-way beyond the orifices of their respective tubules ; flagella equal 

 to r exceeding twice the length of the body; contractile vesicle con- 

 spicuous, subcentral. Length of bodies 1-3000", height of zoothecium 

 1-300". HAB. Fresh water. 



The two colonies of this species figured by Stein,* here reproduced, differ 

 remarkably, the tubular ramuscules in one example being perfectly straight, and 



1 Infusionsthiere,' Abth. iii., 1878. 



