SCIENCE-GOSSIP. 



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vestibulum, the left one being more or less convo- 

 lute round an elevated and protrusible central 

 area which constitutes the so-called ciliary disc ; 

 vestibulum continued backwards into the sub- 

 stance of the body as a conspicuous cleft-like 

 pharynx, and often further prolonged as a narrow 

 tubular oesophagus." 



Genus Vorticella. — All the species of the 

 genus are sessile ; the body is bell-shaped, the 

 broad end of the bell is distal, the narrow proximal 

 end being attached by means of the stalk, down 

 which runs the contractile " muscular band." The 

 distal broad end is probably homologous with the 

 ventral side of other Ciliata. Its edge is raised up 

 all round into a kind of lip — the peristome. Imme- 

 diately inside the peristome, at one point, is a 

 depression — the vestibulum. From the vestibulum 

 a conspicuous pharynx leads into the body 

 substance ; it is continued by a narrow oesophagus 

 which runs still further in. The central part of the 

 distal area is raised into an elevation called the 

 ciliary disc. A groove — the peristomial canal — 

 runs between the disc and the peristome, of which 

 the vestibulum is merely a local enlargement. 

 A band of cilia starts in the pharynx, runs up the 

 pharynx and vestibule, and then turns to the left 

 and runs along the inner side of the peristome ; it 

 is further continued round the ciliary disc. The 

 mouth lies at the end of the oesophagus. Ingested 

 particles of food make two complete turns right 

 round the animal and then come out by the anus, 

 which is situated on the wall of the pharynx. The 

 contractile vacuole is spherical, and on contraction 

 sends its contents into an oval reservoir which 

 opens into the pharynx near the anus. The 

 macronucleus is long and band-shaped; a small 

 micronucleus is placed near it. Delicate " myo- 

 phan " striations radiate from the attachment of 

 the body to the stalk. Vorticella is exceeding sensi- 

 tive, and retracts itself immediately when irritated, 

 and often without any apparent irritation. This 

 retraction is brought about as follows : the muscu- 

 lar band in the stalk mentioned above contracts 

 and draws the stalk down into a tight and regular 

 spiral ; the disc is drawn in and the peristome is 

 drawn up over it, all round, so as to completely 

 cover it up and to shut the aperture of vestibule. 

 These sudden contractions are very inconvenient to 

 the microscopist, as the expansion is a compara- 

 tively slow process. I have come across Vorticellae 

 which seemed to be in a perpetual state of expan- 

 sion or contraction. They were most distracting. 



The reproduction takes place by oblique fission. 

 Under ordinary circumstances, the products of 

 fission consist of a sessile individual and a free- 

 swimming individual. The former resembles the 

 mother animal ; the latter is like it also in general 

 structure, but has no stalk, and is girded round its 

 aboral end with a circlet of swimming cilia. When 



swimming about it keeps its mouth shut, that is to 

 say, the disc is retracted and the peristome drawn 

 over ; it can thus take in no nourishment. It soon 

 settles down on its aboral surface, loses its swim- 

 ming cilia, and develops a stalk, opens its mouth 

 to take in food, and becomes in fact an ordinary 

 Vorticella like its parent. In some cases I have 

 observed two free-swimming individuals to result 

 from oblique fission. Conjugation takes place in 

 a peculiar way : an individual divides into two 

 halves, one of these remains on the stalk, the 

 other divides again into from two to eight daughter 

 cells, which resemble in structure the free-swim- 

 ming form produced by ordinary fission, but are 

 much smaller. These daughter cells swim freely 

 till they come to an ordinary sessile individual, 

 with which they pair. The product of fusion 

 divides immediately, and its activity is in all 

 respects increased. 



There are numerous species known of the genus 

 Vorticella which agree pretty well with the generic 

 description given above. Three species will be 

 found mentioned here. 



Vorticella alba de Fromentel. — The body of this 

 species is about one and a-half times as long as 

 broad. The surface is not marked by any striae. 

 The protoplasm is remarkably clear. The length 

 of the body is about 70 microns ; the stalk is 

 about three to five times this length. 



I have found this form living in aquatic plants 

 and have also obtained some specimens on Cyclops. 



Vorticella microstoma Ehrenberg. — The body is 

 very variable, but is generally much the shape of 

 V. alba. The cuticle is marked with transverse striae ; 

 the stalk runs into a kind of sheath of body sub- 

 stance ; the pharynx is longer than usual. The 

 length of the body is from 30 to 100 microns. 

 The stalk is from two to six times as long as this. 



The animal may be found growing on weeds in 

 fresh water. 



Vorticella nutans Muller.— The peristome in this 

 species is everted, and separated by a constriction 

 from the rest of the body. The cuticle is smooth. 



Fig. 36.— Vorticella nutans, 

 pe, peristome ; d, ciliary disc ; vent, vestibulum ; ph, 

 pharynx ; oes, oesophagus ; lettering otherwise the same as 

 in the preceding figure ; aa, are expanded individuals from 

 two points of view ; b, a contracted individual. 



