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 Vkoooth 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 ANIMAL- 

 CULES. Some of these build 

 up tree-like growths by re- 

 peated subdivisions and im- 

 perfect separation, 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 NoCTI- 

 LUCA, 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 

 extended notice. It is to the 

 presence of the Noctiluca in 



fhatb, W. Savill.-Ktnt, F.Z.S.] 



CUP-SPONGES, PHOTOGRAPHED AS GROWING 

 IN A CORAL-POOL 



The Neptune* 'i-cuf Sponge, allied to this species, /j mutimei 2 ur j Jeet in height 

 and diameter 



