OF THE ASTASIA A OE EFGLEN^A. 



545 



cliMuens of Miiller. All the species are exquisite objects for a deep-powered 

 microscope — for instance, one magnifying 460 diameters. Perty unites this 

 genus with Astasia, as being indistinguishable from it by any sufficient charac- 

 teristics. 



DiSTiGMA tenax {ProUus, M.). — Larger 

 than either of the other species ; proteus- 

 like — at one time greatly distended, at 

 another as much consti-icted ; eye-speck 

 rather indistinct ; colour transparent yel- 

 low. About liCmnse. 1-240". This spe- 

 cies Perty regards as merely a larger 

 variet}^ of Astasia margaritifera, inca- 

 pable of the same extent of metabolia. 



D. Proteus (Proteus, ~M.). — Smaller than 

 the preceding ; proteus-like — sometimes 

 greatly distended, at others constricted ; 

 blunted at both extremities ; eye-specks 

 distinct. Amongst Confervae. 1-580" to 

 1-400". This species, says Perty, appears 

 nothing else than a smaller specimen of 

 Astasia margaritifera which has lost, to 



a greater or less extent, its filaments, and 

 therewith its power of swinmiing, whilst 

 it retains the remarkable peristaltic move- 

 ments in its internal substance. 



D. viriclis. — Smaller than either of 

 the other species; proteus-like some- 

 times greatly distended, at others con- 

 stricted ; filled with gi'een granules ; eye- 

 specks distinct. Length not exceeding 

 1-570". D. viridis is,inPerty's opinion, an 

 incomplete condition of Eutrei)tia viridis. 



D. planaria. — Small, linear; proteus- 

 like, but capable of less distension or 

 constriction than the preceding ; pointed 

 at both exti-emities ; colourless; eye- 

 specks distinct. Found by Ehrenberg 

 amongst Confervaa in the Nile. 1-240". 



Genus PEEANEMA (Duj.) (XXYI. 13).— Body of variable form, some- 

 times almost globular, at others distended posteriorly, and drawn out in front, 

 or prolonged into a long tapering filament. Movement forwards slow and 

 uniform. The Peranemce are colomdess, but contain in theii' diaphanous 

 substance granules and vacuoles. The lobes they send out in their frequent 

 and remarkable changes of form are, unlike those of the Amcehce, covered 

 with an integument. Found in stagnant marsh- water, chiefly on the surface 

 of dead plants. I suspect Ehrenberg has described a species (P. lyrotracta) 

 of this genus under the name of Traclielius trichopJiorus. 



Pebanema protracta. — Oblong, soft, 

 dilated posteriorly, much extended an- 

 teriorly. 1-838" "^to 1-370". Its figure 

 undergoes changes by the movements of 

 its contents. A trace of a red stigma 

 often discoverable. 



V. glohdosa (xxvi. 1.3). — White or 

 pale-green, nearly globular, more or less 

 extended anteriorly, with oblique plaits 

 on its surface. In the Seine, and in 



ponds at Bern. 1-1625" to 1-1300". Perty 

 could not discover the plaits or folds, 

 and states that the filament is double 

 the length of the body. Movements 

 ver}' active. 



P. virescens. — The animalcule so named 

 occurred in the water of the Seine, was 

 green, semi-fluid, and changed fonn most 

 rapidly, like stnAmaba. 1-860" to 1-520". 

 Requires further examination. 



Genus ZYGOSELMIS (Duj.) (XXYI. 12 a, 6).--Animal of variable form, 

 swimming by means of two equal flageUiform filaments, which are constantly 

 in agitation. Zggoselmis, says Dujardin, is distinguished from Diselmis by 

 its contractility and its variabihty of form ; but such a distinction is siu'ely 

 insufficient. 



Zygoselmis nehulosa (xxvi. 12 a, b). — 

 Colourless, sometimes globidar, at others 

 top- or pear-shaped, vnth nmnerous con- 

 tamed granules. 1-1300", with two fila- 

 ments of equal size and length. Un- 

 common; found with Lemna; the changes 

 of form proceed slowly. 



Z. in(equalis (Perty)!! — Colomless, hya- 

 hne; one filament rather stouter than 



the other ; both protruded in front. Ca- 

 \\tj sometimes filled with clear green 

 corpuscles, which frequently assume op- 

 tically a red hue. Changes of figure 

 slow ; movements sluggish. Distin- 

 guished from Z. nebulosa by the inequa- 

 lity of its filaments. 1-840". The assigned 

 distinction between this and the other 

 species appears to us insufficient. 



Genus HETEROXEMA(Duj.) (XXYI. 11).— Body of variable form, oblong, 

 irregularly dilated posteriorly, having a fine flageUiform filament, and a second 



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