286 ORDER FLA GELLA TA-PANTOSTOMA TA. 



on a slightly reduced scale, there are no less than two hundred tubules bound together 

 in the flabelliform zoothecium, about one-half of these only, however, being occupied 

 by their minute fabricators. 



Rhipidodendron Huxleyi, S. K. PL. XVI. FIGS. 4-9. 



Aggregated tubules forming a spreading, bush-like, rust-brown, dichoto- 

 mously branching, granular zoothecium, each separate branchlet of which 

 is normally composed of four laterally united tubules ; animalcules 

 elongate-ovate, about twice as long as broad, scarcely projecting beyond 

 the apertures of their respective tubules ; flagella of equal size, twice the 

 length of the body, inserted close to one another at the anterior extremity. 

 Length of zooids 1-4000", diameter of adult bush-like zoothecium i-io". 



HAB. Bog water. 



This second species of the genus Rhipidodendron represents one of the latest 

 acquisitions chronicled in this treatise, it having been collected by the author in 

 September 1879 at Lustleigh Cleave, on the borders of Dartmoor, S. Devon; the 

 same bog water yielding also the two new forms hereafter described under the titles 

 of Spongomonas sacculus and Monosiga longicollis. 



From the preceding type the present species may be at once distinguished by 

 the attenuate form of growth of the zoothecium, only four tubules, as a rule, instead 

 of a large and indefinite number, being bound up together in each separate ramus- 

 cule. The manner in which this more symmetrically branching zoothecium is con- 

 structed, is made apparent by reference to the diagrammatic illustration given at 

 PI. XVI. Fig. 8. As there shown, all four of the monads inhabiting the primitive 

 four- chambered ramuscule divide by longitudinal fission simultaneously and abreast 

 of one another, the result being the production of eight in place of the preceding 

 four ; the lateral pressure thus brought to bear within the comparatively confined 

 space causes each equal moiety of four zooids to diverge slightly from the other, 

 and these continuing independently the fabrication of their granular sheath, pro- 

 duce, at more or less regular intervals, the characteristic bifurcation of the entire 

 mass. The absence of symmetrical subdivision of the zoothecium in R. splcndiJmn 

 is explained by the fact that the component tubules are congregated in rows two or 

 three deep, the monads evidently not separating persistently in the same plane as 

 obtains in the present type. The rust-brown, bush-like zoothecia of this species 

 were produced abundantly, in close proximity to those of Spongomonas sacculus, on 

 the sides of the bottle of water brought from the locality quoted, remaining so 

 attached and forming conspicuous objects to the unaided vision for several weeks. 

 Fragmentary branches of the zoothecia of a species identical with, or closely allied to, 

 the present form, but exhibiting less regularity in the combination of the individual 

 tubules and plan of bifurcation, have been recently received by the author from 

 Mr. J. Levick, of Birmingham. 



GENUS III. SPONGOMONAS, Stein. 



Animalcules evenly ovate or spheroidal, provided with two equal-sized, 

 anteriorly inserted, vibratile flagella ; living in social colonies, and forming 

 by excretion a common domicile, which takes the form of a variously 

 modified gelatinous or semi-granular zoocytium, within which they remain 

 constantly immersed, their flagella only protruding into the outer water ; 

 contractile vesicle and endoplast usually conspicuous ; no distinct oral 

 aperture. Inhabiting fresh water. Increasing by longitudinal fission and 

 by the subdivision of the entire body into sporular elements. 



