72 



MORPHOLOGY. 



and the external cliitinous capsule. In the cavity which occupies the interior of the soft contents 

 of the capsule very distinct rotating currents may be now seen, excited, doubtless, by the action of 

 vibratile cilia, though a direct view of these cilia cannot be obtained through the thickness of the 

 walls. 



Fig. 33. 



Development of Hydranth and Hydrotbeca in Laomedea flexuosa. 



a. Very early condition, in which the bud forms a simple cylindrical csecal oflset from the 

 coenosome. 



J. The distal extremity of the bud has become enlarged, so as to present the form of an 

 inverted cone. 



c. The cone has increased in size, and the soft parts towards its proximal end have become 

 retracted from the external chitinous walls. 



d. The internal structures have still further withdrawn themselves from the chitinous walls, 

 with which they are uow in contact only by a narrow proximal and a wider distal zone, between 

 which they present the form of a tubular cylindrical column. 



e. The distal zone of contact has become retracted from the summit of the cup-like_ envelope 

 of chitiue, tentacles have begun to sprout from its circumference, and a hypostome has risen from 

 its centre. The leading features of the completely formed hydranth are thus established, and its 

 chitinous envelope has become the hydrotbeca. 



The arrows in the figures indicate currents in the somatic fluid. 



Between the proximal and distal zones of contact the internal structures become more and 

 more withdrawn from the walls of the capsule, while the whole body continues to elongate {d) ; and 

 this may now be seen in the form of a cylindrical column occupying the axis of a conical cup of 

 chitine, and expanded below into a narrow ring, which at this point connects it with the walls of 

 the cup, while above it expands into a broad disc, which fills up the distal extremity of the cup 

 like a lid or plug. The axis of the column is permeated by a tubular cavity in continuation 

 below with the cavity of the branch, and expanding above into a wide chamber, which occupies 

 the interior of the plug-like enlargement of its distal end. It is now plain that, while 

 the soft contents of the cup are the developing hydranth, the cup itself is to become the 

 hydrotbeca. 



The excreting of the chitine and the shaping of the hydrotbeca would seem to devolve on 

 the terminal plug-like disc alone, from the time that the lower parts of the nascent hydranth liad 

 withdrawn themselves from contact with the walls of the external capsule ; and as the hydranth 

 continues to elongate itself, the surrounding cup is extended at the same rate, by addition 

 to its wider end from the sides of the disc, while the lower parts of the cup undergo little or no 

 change. 



