164 



CCELENTERATA. 



sion of the common canal, is termed the " radicle/' or " initial 

 point," as marking the organic base of the frond. 



The " common canal " is the tube in which the coenosarc 

 was enclosed ; but it commonly appears, in compressed speci- 

 mens, merely as a vacant space between the " cellules " and 

 the solid axis. The common canal gives origin, by a process 

 of budding, to the " cellules " or " hydrothecse," which are 

 little horny cups for the reception of the polypites. Each 



Fig. 55. A, Young individual of Monograptus Sagittarius, His., showing the slender 

 curved base of the frond, and the extension of the axis beyond its opposite end ; B, Base of 

 another individual of the same, in which there is an extremely long "radicle;" c, Frag- 

 ment of M. Sagittarius, much enlarged to show the cellules from a specimen in relief; 

 D, Specimen of Monograptus Clingani, Carr., showing the distal and proximal extensions 

 of the axis. 



cellule rests by its base upon the common canal, is separated 

 from its neighbours by " cell-partitions/' and opens at its 

 apex by a distinct aperture or " cell-mouth," through which 

 the polypite could exsert its tentaculate head. 



The reproductive process appears, in some cases at any 

 rate, to have been carried on by the formation at certain 

 seasons of horny capsules, of much greater size than the 

 cellules, within which the generative elements were matured. 

 In some cases these " ovarian vesicles " have been found 

 actually attached to the fronds of Graptolites. In other 

 cases, as described by the writer, we find numerous bell- 

 shaped horny capsules, termed " Daivsonice" (fig. 56), each 

 with a little spine at its summit, scattered through the rock 



