414 ORDER FLAGELLATA-EUSTOMATA. 



Genus XV. UROGLENA, Ehrenberg. 



Animalcules enclosed socially within a subspheroidal gelatinous matrix 

 or zoocytium, to the centre or deeper substance of which they are united 

 through the medium of slender, thread-like, highly contractile, posteriorly 

 developed prolongations ; in their normal or extended condition the anterior 

 borders of the individual animalcules impinging upon or projecting slightly 

 beyond the periphery of the zoocytium, but capable at will, through the 

 contractions of the filiform posterior prolongations, or pedicles, of being with- 

 drawn entirely within its substance ; flagella two in number, of diverse 

 size ; endoplasm enclosing two distinct lateral colour-bands, and usually one 

 or more eye-like pigment-spots. Inhabiting fresh water. 



Uroglena volvox, Ehr. Pl. XXIII. Figs. 4-15. 



Colony-stocks subspherical or more or less asymmetrical ; bodies pyri- 

 form, the anterior border rounded, somewhat obliquely truncate, taper- 

 ing posteriorly, and thence continued backwards in the form of a long, 

 slender, hyaline, and highly contractile thread-like prolongation; lateral 

 pigment-bands yellowish-green, of uneven length ; eye-like spot single, 

 situated anteriorly and in the median line, close to the base of the two 

 flagella ; flagella of conspicuously diverse size ; contractile vesicles two in 

 number, located close together near the centre of one of the lateral borders ; 

 a large ovate and apparently amylaceous corpuscle mostly developed 

 towards the posterior half of the body. Length of bodies 1-1200", average 

 diameter of social colony-stocks 1-90". Hab. — Pond water. 



This type, in common with Synaypta, Syuwa, and other socially aggregated 

 Chloromonadidse, has been usually regarded as a doubtful form probably representing 

 an imperfect or transitional condition only of the protophytes Volvox or Sphcerosira. 

 Quite recently, however, it has been shown by both Biitschli and Stein, to be an 

 independent organism exhibiting, with relation to the form and characters of the 

 individual zooids, an entire conformance with the several other generic types com- 

 prised in the Chrysomonadid?e. Examples of this species were likewise remitted to 

 the author during the month of June 1879, hy Mr. H. E. Forrest and Mr. Thomas 

 Bolton, from the neighbourhood of Birmingham, the result of such a personal 

 acquaintance with it being the discovery of various supplementary structural and 

 developmental phenomena here recorded for the first time. More especially in this 

 connection may be mentioned the establishment of the possession by the zooids of 

 a posteriorly developed thread-like pedicle, first imperfectly observed and inter- 

 preted by Ehrenberg as a simple tail-like prolongation, but entirely overlooked by 

 both Stein and Biitschli. This structure is, in fact, so slender and transparent as to 

 require a high magnifying power, 600 to 800 diameters, and the nicest adjustment of 

 the illumination for the demonstration of its existence. Such conditions being 

 secured, however, its presence is conspicuously apparent both in living examples and 

 in specimens treated with osmic acid and permanently preserved. Under the latter 

 auspices, indeed, this special structure may perhaps be most readily identified, 

 though its contractile properties and complete conformity with the contractile pedicles 

 of Dinobryon and Epipyxis are recognizable only in the living state. 



Among the data observed by the author with reference to the reproductive 

 phenomena, it has to be recorded that zooids were abundantly found withdrawn 

 into the common matrix or zoocytium, devoid of flagella, and presenting every step 



