MOSS ANIMALS 



3393 



of tentacles, which is also a gill, is horseshoe shaped, and the whole 

 Order surrounded at its base by an integument forming a kind of calyx or cup. 



y ac- ^ke chambers or cells are either quite soft or else horny, and are thus 

 tolaemata 



not found in a fossil condition. Later on in this volume is described 



a colony of sea anemones which, instead of being fixed, as are most stocks, are 

 able to travel about; a colony of moss animals capable of locomotion is figured 

 on p. 3396. These remarkable moving types (Cristatella) form flattened, 

 elliptical colonies, which creep 

 along on a kind of flat foot, follow- 

 ing the direction of the light. 

 The question may be raised as to 

 how the many separate individuals 

 manage to move in the same 

 direction. Even if an external 

 stimulus, such as light, should 

 stimulate the individuals in the 

 same way, this seems hardly 

 sufficient to account for the 

 movement of the colony, without 

 some nervous system connecting 

 the polyps and co-ordinating the 

 movements of the colony. As a 

 matter of fact, such a system does 

 exist. While each separate animal 

 is provided with a nerve ganglion 

 between the oesophagus and the 

 posterior opening of the alimentary 

 canal (c in the illustration on p. 

 3391), and with the nerves neces- 

 sary for its own individual organ- 

 ization, the Bryozoan colony, as 

 such, has a special nervous system 



which is connected with the individual systems, and runs from one to another 

 through the apertures by means of which also the body fluids circulate throughout 

 the colony. This colonial nervous system no doubt regulates the movement of the 

 stock. 



In contrast to the Phylactolaemata are the Gymnolaemata, those 

 Bryozoa in which there is no lid to the mouth, and in which the ten- 

 tacles are arranged in a circle on a disc instead of in the shape of a 

 horseshoe; the name given to such forms denoting the naked con- 

 dition of the mouth. These naked-mouthed Bryozoans are far more numerous than 

 those with lids to their mouths. Paludicella which is fully described on pp. 3390, 

 3391, is one of the few fresh- water forms belonging to this order. Here, the crown 

 of tentacles cannot be completely protruded, and thus appears even when most ex- 

 tended, to be surrounded by a double collar. A numerous group of this order are 

 213 



LACE CORAL, Lepralia. 

 (Natural size.) 



Order 



Gymno- 

 laemata 



