ON THE DEVELOPMENT OF TUBULIPOEA. 103 



marked, as Smitt points out. The zooecia are relatively large, 

 averaging about 175 /i iu diameter. 



The Goeciostome more nearly resembles that of T. plumosa 

 than that of the other species here described, but it differs 

 from it in the fact that the basal region of the tube, which is 

 perforated by pores, is commonly partially free (fig. 3), whereas 

 in T. plumosa, as in T. phalangea and. T. liliacea, the 

 porous part is wholly adnate to a zooecium, and only the non- 

 porous termination of the tube is free. The ooeciopore typically 

 opens upwards, or away from the basal surface of the colony. 

 The proximal part of the tube is attached to a zooecium, and is 

 followed by a considerable free length of tube (part of which is 

 porous), which dilates upwards, so as to be more or less funnel- 

 shaped. This funnel-shaped portion commonly grows away 

 from the first zooecium and towards the free part of a second 

 zocEcium, on which its edge rests. In T. plumosa the whole 

 of the tube is recumbent on the same zooecium or zooecia. In 

 some specimens of T. aperta, and especially when the tube is 

 wedged in between two zooecia which are near one another, 

 the arrangement above described is not so obvious. The ooecio- 

 pore is circular or oval, and is of considerable size, its longer 

 diameter usually varying from 200 fx to 370 }x, and averaging 

 about 280 jx. One abnormally small ooeciopore was only 135 jx, 

 and one unusually large one was 435 ^, but the usual range is 

 given by the figures first stated. The edge of the ooeciopore 

 may be slightly everted, or evenly circular or oval. In some 

 cases it is somewhat indented on one or both sides, and may 

 then closely resemble that of T. plumosa. 



In one or two colonies the proximal part of the exposed 

 portion of the ovicell had the characters of an ordinary zoce- 

 cium, the pores being very few and widely scattered. At the 

 level where the ovicell commences to enlarge, in these cases, 

 the pores become suddenly numerous, and the zooecium takes 

 on the character of an ovicell. The line where the pores 

 become more numerous probably corresponds with a time at 

 which the embryonic structures reached a certain stage of 

 development. The same peculiarity in the ovicell was also 



