220 MODE OF GROWTH OF THE RADIATES. 



young developing most actively at the end of June. Unlike Ac- 

 tinia, which is always hermaphrodite, this coral is rarely so, but 

 the polypes of different branches belong to different sexes. 



As in the other polypes, including Actinia, the eggs and sper- 

 matic particles rupture the walls of their respective glands situ- 

 ated in the fleshy partitions. As in Actinia, Lacaze-Duthiers thinks 

 the fecundation of the egg occurs before it leaves the ovary, when 

 also the segmentation of the yolk must take place. Unlike the 

 embryo Actinia, the ciliated young of the coral, after remaining 

 in the digestive cavity for three or four weeks, make their way out 

 into the world through the tentacles. " Many times," says Lacaze- 

 Duthiers "have I seen the end of the tentacle break and let out 



the embryo." The appearance of the embryo, when first ob- 

 served, was like that in Fig. 77, A, an oval, ciliated body with a 

 small mouth and a digestive cavity. This may be called the gas- 

 trula, adopting Haeckel's phraseology. 



The gastrula changes into an actinoid polype in from thirty to 

 forty days in confinement, after exclusion from the parent, but in 

 nature in a less time, and it probably does not usually leave the 

 mother until ready to fix itself to the bottom. 



Before the embryo becomes fixed and the tentacles arise, the 

 lime destined to form the partitions begins to be deposited in 

 the endoderm. Fig. 77, C, shows the twelve rudimentary septa. 

 These after the young actinia, or "actinula" (Allman), has be- 

 come stationary, finally enlarge and become joined to the external 



