ON THE DEVELOPMENT OF TUBULTPORA. 139 



times the length of the embryo in fig. 19. Several giant-cells 

 are seen in the immediate neighbourhood of the embryo, as in 

 Crisia and Lichenopora, The function of these is not 

 certain, but there is no evidence that they take any direct part 

 in the future development. 



The cavity of the embryophore has greatly enlarged, and 

 now fills up most of the ovicell. Parts of the nutritive tissue 

 are seen in its proximal region, and a fevr scattered cells 

 belonging to this tissue occur in the middle of the cavity. 

 The brown body is at the distal end of the cavity ; and this is 

 its usual, though not its invariable position. In some cases, 

 during this or earlier stages, it may lie partly in the cavity of 

 the embryophore and partly in the vestibule, demonstrating 

 the existence of a communication between these two cavities. 

 The vestibule is much shorter than before, so that the distal 

 end of the cavity of the embryophore is now very near the 

 terminal membrane. The point where the vestibule joins the 

 terminal membrane will become the future ooeciopore, the 

 morphological " orifice ^^ of the ovicell. 



The terminal membrane is still a good deal thickened and 

 folded at its edge, particularly on the left side of the section, 

 and it contains the usual excretory vesicles. 



The general features of stage E are thus as follows : — The 

 fertile zooecium becomes definitively an ovicell, and becomes 

 obvious externally by the dilatation of its distal end. The 

 part of the embryophore immediately distal to the follicle be- 

 comes more or less hollowed out, so that a passage is prepared 

 by which the embryo can pass into the nutritive tissue, which 

 is developed from the proximal part of the investment of the 

 brown body. The part of the embryophore containing the 

 nutritive tissue becomes vacuolated, and finally forms a wide 

 space. 



The brown body is generally left at the distal end of this 

 space, surrounded by a mass of cells in close connection with 

 the vestibule ; but as by the vacuolation of the surrounding 

 tissue it becomes free from other tissues, its position towards 

 the end of this stage is variable. It may pass into the proximal 



