262 



C(ELE>*TEEATA. 



Gf 



R 



2)ossess an wsopli.ayeal tube and a yastro-vascular canal system. Two 



lateral tentacles, which can be retracted into pouches, are often present. 



The Ctenopliora, possess a shape which can in all cases be 



reduced to a sphere. They are radially symmetrical free-swim- 



ming Coelenterata of gelatinous 



consistence. The body is often 



bilaterally compressed, so that it is 



possible to 



distinguish 



two planes 



passing 



through the 



long axis at 



right angles 



to one an- 



FIG. 201. Cydippe, seen from the 



apical pole, s, Sagittal plane ; T, other : these 

 transverse plane; X, swimming are the*W/^- 

 plates ; Of, gastro-vascular system. 



tal plane and 



the transverse plane, and are analogous 

 to the median (longitudinal vertical), and 

 lateral (longitudinal horizontal) planes of 

 bilaterally symmetrical animals (tig. 201). 

 The arrangement of the internal organs 

 bears a relation to these two planes. All 

 parts of the body which occur in pairs, as 

 the two tentacles, the gastric canals, the 

 hepatic bands of the stomach, and the 

 vessels which give origin to the eight lateral 

 canals, all lie in the transverse plane, while 

 the sagittal plane coincides with the longer 

 axis of the oesophageal (gastric) tube (whence 

 also called the gastric plane), the two so- 

 called polar-fields, and the terminal vessels 

 of the infundibuluui. 



- 



The inf undibulum is so compressed that FlG zaz.Ct/iHp 

 its longest diameter falls in the lateral ;'''"'-' 0^ Chnn )- 



Mouth. 



plane, which on this account is sometimes 



called the infundibular plane. Since these two planes divide the body 

 into halves, which correspond with one another, and since there is no 

 division into dorsal and ventral surfaces, the arrangement of the 

 body may be said to be bi-radially symmetrical, but cannot be called 



