148 SIDNEY F. HARMER. 



ooeciostome, where the vestibule opens to the exterior ; and the 

 secondary embryos ultimately escape by this passage. 



The junction of the embryophore with the vestibule is some- 

 what complicated, and from stage D onwards there is a 

 cellular plug between the brown body and the vestibule. This 

 is shown in fig. 20 {y.), where it is still solid. In a later stage 

 (fig. 22, y.) it becomes hollow, its cavity sometimes appearing 

 completely closed, sometimes opening towards the brown body, 

 and sometimes communicating with the vestibule. These 

 different conditions appear to be found in ovicells of one and 

 the same stage, and the first of them is shown in fig. 25. This 

 figure illustrates the way in which the wall of the embryo- 

 phore is reflected inwards, and the similarity with a polypide- 

 bud (fig. 23) is marked. 



It is possible that this plug of cells is the morphological 

 representative of a tentacle-sheath. On this view, the brown 

 body of fig. 25 does not lie freely in the tentacle-sheath (which 

 would be a somewhat anomalous position for it to occupy), but 

 in the body-cavity. 



Sooner or later the vestibule becomes continuous with the 

 "tentacle-sheath" (y.), and this with the body-cavity; the 

 communication between the two latter being uninterrupted 

 after the migration of the brown body to some other part of 

 the body-cavity. A communication between the body-cavity 

 and the exterior is not a very unusual occurrence in the 

 Polyzoa, since the reproductive bodies escape more or less 

 directly from the former to the outside in several cases. This 

 is shown, in Phylactolsemata, by the escape of the statoblasts 

 after the decay of the polypide has left an open passage to the 

 exterior, and in certain Gymnolsemata by the occurrence of a 

 special passage, the intertentacular organ. 



The cavity of the embryophore in Lichenopora is probably 

 comparable with the cavity in Tubulipora. The stage shown 

 in pi. ix, fig. 27, of my former paper (16) is very similar to a 

 Tubulipora at the end of stage D, The vestibule is repre- 

 sented by the invagination there marked " orifice ; " the brown 

 body with its investment requires no special explanation, while 



