766 



The Living Animals of the World 



has a distinct throat-opening, two rhythmically contracting cavities fulfilling a respiratory 

 function and a complex reproductive nodule, or nucleus. Compared with a host of its kindred, 

 this animalcule is a giant, the longest diameter of many of the smaller varieties measuring 

 no more than the -j^Vffth part of inch, or even less. 



The elegant little BELL-ANIMALCULE, with its crystal wineglass-shaped body, crown 

 of vibrating hairs, and long spirally contractile foot-stalk, is a familiar object to the 

 possessor of a microscope. Most commonly these single-celled organisms, like the single- 

 celled elements of organic tissues, multiply by repeated sub-division, the number that 

 can be reproduced in a short space of time by this simple process being almost 

 incredible. As many as a million, it has been calculated, of some species may be 

 thus derived from an original single individual within twenty hours. In this connection 

 these lowly organisms can among living animals most logically lay claim to immortality. 

 The individual, in point of fact, never dies. Finding itself growing old and obese at 

 the ripe age of, say, sixty minutes, it has simply to split itself up into two offsets, 

 which swim away and repeat the process. Occasionally, for the rejuvenescence of the 

 race, two individuals coalesce completely with one another, and multiplication by splitting 

 takes place. 



Some near relations of the little bell-animalcule, while sub-dividing so far as their bodies 

 are concerned, remain united by their foot-stalks, and thus in time build up beautiful tree- 

 like structures, laden as it were with crystal bells or fruit. In some of these the common 



branching foot-stalk is erect and rigid, while in others it is flexible, and contains, as in the 



ordinary species, a central elastic ligament. Under these circumstances the whole tree-like 



structure, with its crystal bells, collapses and expands again under the slightest stimulus, and 



constitutes one of the most 



beautiful objects that can be 



viewed through the microscope. 

 In lower forms of the 



infusorial animalcules one or 



more long, lash-like organs take 



the place of locomotive hairs. 



In this category are included the 



COLLAR-BEARING ANIMALCULES. 



Some of these build up tree- 

 like growths by repeated sub- 

 divisions and imperfect separa- 

 tion, after the manner of the 



bell-animalcules, while others 



excrete tubular dwelling-cases, 



inhabited by the resultants of 



the splitting process. Such 



forms can with difficulty be 



distinguished from skeletonless 



sponges. 



. The animalcule NOCTILUCA, 



which by its countless 



myriads is the chief constituent 



of ocean phosphorescence, is a 



member of the Lash-bearing 



group. This noteworthy form 



invites a somewhat more Photo by w ' 



extended notice. It is to the CUP-SPONGES, PHOTOGRAPHED AS GROWING IN A CORAL-POOL. 



Of the Noctiluca in The Ne P tune ' s ' cu P s P n g e > allied to this species, is sometimes 2 or 3 feet in height and 



diameter. 



