ON THE DEVEL0PM1':NT of TUBULIFORA. 141 



Ilia case of rapid and continuous growth like tliat of the 

 ovicell of Tubulipora there is of course no special signifi- 

 cance in the measurements quoted, but they will give some 

 idea of the dimensions of the parts during the stage in ques- 

 tion. The measurements here given refer to T. plumosa. 



Throughout stage E the embryo is found at the proximal 

 end of the embryophore. At first in its follicle, the embryo 

 begins to extend into the adjacent part of the embryophore as 

 it begins to lengthen. Later in the stage it lies somewhat 

 more distally in the embryophore, its long axis coinciding 

 with that of the ovicell. The distinctness of the follicle be- 

 comes lost towards the end of this stage, and the fertile brown 

 body diminishes in size. 



Stage F. — Commencement of Embryonic Fission. 



I have not given any figure of this stage, which does not 

 diflfer materially from that of Licheuopora. The primary 

 embryo increases largely in size, and divides in much the same 

 way as in that genus (see 16, pi. x, figs. 32 — 35). 



The details of the lobing of the ovicell are not always the 

 same, as is shown by the varying position of the oceciostome 

 in the adult ovicell ; but in several cases which I have observed 

 in stage F the distal end of the embryophore was merely a 

 later stage of the oldest embryophore, with a trefoil-like 

 lumen, described in stage E. This trifid division of the 

 embryophore is certainly a common arrangement, the median 

 lobe being connected with the vestibule, and therefore later 

 with the oceciostome ; while the other lobes form the more 

 lateral parts of the ovicell. The lobe connected with the 

 vestibule may be termed the " axial lobe,'^ because, although 

 not necessarily in the axis of symmetry of the ovicell, it is 

 part of its morphological long axis. Other lobes will be 

 termed '* lateral lobes." 



Ovicells in stage F may exhibit no subdivision of the primary 

 lobes, but in other cases the end of each of the lateral lobes 

 becomes bilobed. This subdivision of the embryophore is in 



