1888.] MICROSCOPICAL JOURNAL. 61 



and surrounded by a drop of water. This passage is, as a rule, conspic- 

 uously visible only while the food-globule is traversing it, although, in 

 some forms, its walls are ciliated. Careful examination, however, will 

 usually disclose at least some portion of it. The anal aperture opens into 

 the pharyngeal passage, the excrementitious substances being swept out by a 

 sudden and momentary reversal of the ciliary currents. 



The water drop entering the endoplasm with each food-globule must, in 

 some way, be disposed of, otherwise, since the animalcules are voracious and 

 almost insatiable, the body would soon become a mere film enclosing a quan- 

 tity of water. To dispose of this accumulating liquid a contractile vesicle 

 has been developed. This is commonly conspicuous in all the family as a 

 more or less spherical, pale pinkish vacuole, which disappears and slowly 

 returns to its former position at regular intervals. Its contents are supposed 

 to be those water drops which enter the endoplasm with the'food, and to be 

 collected by means of minute channels which are believed to ramify through- 

 out the entire body, transmitting their liquid to this contractile reservoir, 

 whence it is expelled either into the pharyngeal passage or directly into the 

 external water. These drainage canals have not been positively seen ; if 

 they exist, as they probably do, they must be excessively minute, and their 

 walls are probably not lined with a distinct membrane, but consist simply of 

 passages in the soft endoplasm without differentiated boundaries. They may, 

 therefore, be not persistent canals, always holding the same position and tak- 

 ing the same course, but they may be developed at any point in any direction 

 where needed within the parenchyma, and at any time. That the contractile 

 vesicle itself has no lining membrane is the generally accepted belief, yet the 

 propulsive power of the soft endoplasm is such that the vesicle contracts with 

 considerable force. In some of the flagellate infusoria where the contractile 

 organ opens directly into the external water, I have seen the outward cur- 

 rent carry away, in a comparatively violent puff, contiguous bacteria and 

 minute fungous spores, sweeping a clean path before it. In some of the 

 Peritricha there is more than one contractile vesicle in the same individual. 



The entrance and expulsion of the water drops subserve two important 

 functions — those of respiration and excretion. The entering water oxygenates 

 the endoplasm as it circulates, and at the same time carries oft' any gaseous 

 or other absorbable excrementitious materials, bearing the noxious substances 

 to the pulsating vesicle where the vitiated liquid is expelled. 



A second important internal organ is the nucleus. This is usually seen, 

 and without much trouble, as a granular body with refractive properties 

 differing from those of the endoplasm surrounding it. In the Vorticellidas 

 it may take the form of an ovate or subspherical nodule, or of a flattened 

 and variously cui-ved, band-like body. It plays an important part in the act 

 of reproduction. 



The external surface of those animalcules comprising the Vorticellidse is 

 generally a somewhat firm cuticular membrane, often adorned by fine trans- 

 verse striae or other ornamental markings. In some this cuticular coat is so 

 firm that it retains the shape of the zooid after the latter's death, and the 

 escape, by diffluence, of the endoplasm. 



The Vorticellidce are all timid creatures ; a sudden jarring of the table, or 

 a gentle tap against the microscope, or even the unexpected contact of some 

 floating object being sufficient to throw the majority into a spasm of contrac- 

 tion, the ciliary wreaths being quickly folded together and depressed across 

 the ciliary disc, the body drawing itself into as small a compass as possible 

 and crouching against the supporting object, while the entire frontal region is 

 rounded and closfed, so that no vestige of the ciliary apparatus is visible. The 

 loricate and illoricate forms are equally timid, the animalcules within the 



