3o6 



SCIENCE-GOSSIP. 



BRITISH INFUSORIA. 



By E. H. J. Schuster, F.Z.S. 



{Continued from page 203.) 



Part VI. — Ciliata Peritricha. 



'"PHE order Peritricha contains those forms 

 which are characterized by the possession 

 of one or more bands of cilia encircling the body. 

 The Peritricha are sometimes free - swimming, 

 sometimes fixed. In the latter case they generally 

 pass through a free-swimming phase at one period 

 of their life-history. In some instances, however, 

 they can leave their support at any time should 

 danger arise, and swim to some safer place. The 

 sedentary forms may be sessile or stalked, and may 

 have their stalks retractile or non-retractile. They 

 are sometimes solitary, sometimes colonial ; the 

 colonies being often large and tree-like. 



In Butschli's system of classification the Peritricha 

 constitute a section of his order Trichostomata ; 

 but the word is used by him in a narrower sense 

 than by Stein and Saville Kent ; for his section 

 does not include many forms (for example, Uro- 

 centrum, etc.) which are included by the latter 

 authors in their order. The system given in 

 Saville Kent's " Manual of the Infusoria" will be 

 adhered to here, and his diagnoses of the families 

 will be quoted. 



Family Gyrocoridae.— " Animalcules free-swim- 

 ming ; persistent in shape, but not encuirassed, 

 ovate or pyriform ; provided with one or more 

 spiral or circular wreaths of cirrose cilia ; oral 

 aperture lateral or ventral ; anal aperture postero- 

 terminal ; the posterior extremity frequently 

 bearing a stylate, more or less flexuose, caudal 

 appendage." 



Urocentrum turbo Miiller. — The shape of this 

 animal is that of an ellipsoidal piece of india- 

 rubber, round the middle of which fine string 

 has been tightly tied, dividing it into two lobes, 

 anterior and posterior. The mouth is rather large 

 and oval, and lies in the constriction separating 

 the two lobes ; the gullet is long and narrow, and 

 provided with a row of thick-set cilia. The 

 ventral surface is somewhat flattened, and a longi- 

 tudinal groove runs over it from the mouth to the 

 posterior end of the body. The cuticle is thick, 

 and presents a radially striated appearance, due 

 to the presence of trichocysts. The cilia are 

 arranged in two rings, which are easy to see — one 

 encircles the anterior, the other the posterior 

 half of the body. A tail-like structure pro- 

 jects from the hinder end, which sometimes 

 appears to be split up into a number of fibres. 

 The animal is said to anchor itself by this, 

 and thus to assume for a time a sedentary 

 habit. The macronucleus is long and horse- 



shoe shaped, it lies in the posterior lobe of 

 the body ; a small micronucleus is placed by its 

 side. Behind this we find the contractile vacuole, 

 which is a conspicuous feature ; it consists of a 

 central chamber from which radiate four lateral 

 chambers, arranged in a plane at right angles to 

 the long axis of the animal, so that only two can 

 be seen in side view. Figures are given to show 

 the successive shapes assumed by this vacuole. 

 In fig. 35a we have merely the round central 

 chamber exhibited ; in fig. 35ft two of the lateral 

 chambers have begun to appear, followed in 

 fig. 35c by two others ; in fig. 35^ the lateral 

 chambers have increased, the central chamber 

 having, meanwhile, diminished. In fig. 352 the 



Fig' 35- — Urocentrum turbo, 

 ant c, anterior circlet of cilia ; post c, posterior circlet of 

 cilia ; ma n, macronucleus ; mth, mouth ; cv, contractile 

 vacuole ; a, b,c ,d, e, contractile vacuole in successive stages. 



lateral chambers have further increased, and the 

 central chamber diminished. Then the lateral 

 chambers suddenly contract and become lost to 

 sight, as the central chamber again springs into 

 appearance. 



This animal is from 30 or 40 to 100 microns in 

 length ; it is fairly common. I have found it in 

 large numbers in a stagnant ditch, overhung by 

 trees and a hedge, in the neighbourhood of Oxford. 

 It swims rapidly, rotating on its long axis. 



I have found a solution of methylene blue in 

 twenty per cent, alcohol useful in studying it, as it 

 seems to stain, and stop its rapid movements, 

 before absolutely killing it. 



Family Vorticellidae. — "Animalcules most highly 

 contractile ; ovate, sub-cylindrical or campanulate ; 

 sedentary, or temporarily free-swimming ; stalked 

 or sessile ; solitary, or united in social, dendriform 

 or mucus-immersed colonies ; naked, or secreting 

 indurated sheaths or loricae ; oral aperture ter- 

 minal, eccentric, associated with an adoral ciliary 

 spire of one or more convolutions, the right limb 

 of which usually extends into the oral entrance or 



