582 



SYSTEMATIC HISTORY OF THE INFUSORIA. 



ciliarj^ circle. The Stentors are among the largest of the Infusoria, and all 

 the species are visible to the unassisted sight. They are best examined 

 between the plates of a large live-box, a portion of the decayed stem or leaf 

 on which they are found being put in with them. 



" It is," says M. Dujardin, "• in the Stentors where we can view the several 

 supposed internal organs isolately, that new observations will make known 

 theii' real nature." 



They are exclusively found in fresh standing water, or between plants 

 where the water is still. Some of them are colourless, others green, black, 

 or clear blue. 



This genus gives name to the family Stentorina proposed by Lachmann 

 and others, and, in the classification of Dujardin and Perty, is a member of 

 the family Urceolarina (p. 581). 



Stentor MUUeri (xxvni. 16, 17). — 

 This is the " white funuel-like polpye " 

 discovered by Trembley ; it is large, the 

 crown or wreath of cilia interrupted, and 

 the lateral crest or fringe indistinct; 

 when outstretched it is trumpet-shaped, 

 but in its contracted state is ovoid ; and 

 during division, or when the water 

 around it evaporates, a muco -gelatinous 

 mass is thrown out as an external cover- 

 ing. When several are swimming in a 

 glass vessel, they will gradually congre- 

 gate, and select some particular spot, 

 and then attach themselves, evincing, as 

 Ehrenberg imagined, not only a degree of 

 sociality, but of mental activitj^ These 

 animalcules receive coloured food very 

 readily ; nucleus monilifovm. Upon 

 Lemnae and other water-plants, even 



under 



Size, stretched out, 1-20": 



Ehrenberg referred to the exudation of 

 a mucilaginous coat as the prelude to the 

 death of the Stentor ; but, as Cohn has 

 shown {Zeitsclir. Band iii. p. 26.3), it 

 takes place in perfectly healthy and live- 

 ly animals, and is an instance of the 

 widely-pervading process of encystmg. 

 This observer, indeed, tells us that, when 

 the conditions of existence become un- 

 favourable, animalcules preidously at- 

 tached by their tapering posterior ex- 

 tremity, as by a sucker resembling that 

 of a leech, free themselves from their 

 capsular envelope and swim away, dis- 

 playing then a brush of cilia at the end 

 of the tail. The notion of a sentiment 

 of sociality and of mental activity, sur- 

 mised by the Berlin niicroscopist, de- 

 mands the exercise of a powerful imagi- 

 nation to realize it. Dr. Wright most 

 kindly notices, in a letter to us, that 

 Stentor Mi'dlcri always secretes a gela- 

 tinous case into which it can retract. 

 As the zooids divide they form a gela- 

 tinous mass, which is attached to weeds 



and often to the surface of the water, 

 from which 10 or 15 Stentors aggregated 

 together may sometimes be seen hanging 

 with their lieads do\^^n wards. The ex- 

 ternal gelatinous sheath in Stentor and 

 other Vorticellina and Ophrydina, Dr. 

 Wright proposes to call the "coUeto- 

 derni," as the homologue of the gela- 

 tinous matter covering the polypidonis 

 of the Hydroidag. 



^ S. RosseUi (x. 2.33, 2-34).— In form, 

 size, and crest, this species resembles the 

 preceding, but is of a more distinct 

 yellowish-white colour. The nucleus is 

 long, ribbon-shaped, and not monilifonn ; 

 the contractile vesicle (seen at *) circular. 

 Conunon in summer; upon decaying 

 plants, &c., in standing water. 1-liO"; 

 extended, 1-24" 



The monilifonn intestine represented 

 by Ehrenberg was very probably the chain 

 of vesicular dilatations of the presumed 

 vascular system connected with the con- 

 tractile vesicle, and which is largely de- 

 veloped in the Stentors, on one side of 

 the body, as a canal extending from a 

 circular sinus aroimd the head. Dujardin 

 regarded this species as simply a variety 

 of S. MiUleri\ and there is no apprecia- 

 ble character truly distinctive between 

 them. 



S. cceruleus (xxix. 8) resembles, exte- 

 riorly, the two preceding species ; but its 

 granules are blue, nucleus articulated and 

 chain-like (monilifonn). It is trumpet- 

 shaped when extended, ovoid when con- 

 tracted; white or semi-transparent, ex- 

 cept when coloured by food. The lateral 

 crest and frontal wreath are continuous. 

 When kept in glass vessels, they often 

 fix themselves to the sides in chisters. 

 They are best examined when placed in 

 a large live-box ; a magnifying power 

 of 100 diameters is sufficient. Amongst 

 Vaucheri^e. 1-480". 



Except its much smaller size, there 



