Morpliulogy of the Madreporarii. 



4Gi) 



The transverse section dcpicttiJ in fi^. 3 proves that the 

 three or<^ans occur at what is known as the dorsal border of 

 the polyp, one being within tlie dorsal directive entocojle and 

 one within the cxocccle on each side of the directive entocoehi, 

 cxac:ly as described by Krcnipf for the lied Sea Pocillopora'''. 

 In sections of some polyps they occupy nearly the entire 

 mesenterial chamber, while in others they are so enlarged as 

 to result in disturbances of the mesenteries by pressing u{)on 

 theai. 



Fig. 2. 



Vertical section through a polyp. The section pass'\s through tho 

 stomotla'uni, and includes a retracted normal tentacle on the right 

 and a luoditied invaginated tentacle on tlie left. 



An examination of a large number of pol^'ps reveals that 

 the dowiigrowths are not always three in number; sometimes 

 there are only two, and in other instances only one, but never 

 more than three occur. In the polyp represented in section 

 by tig. 4 only one downgrowth is present, situated in the 

 exocade to the right of the dorsal directive entocoele. The 

 polyp is moi*e retracted than that from which tig. 3 was taken, 

 and the intrusion disturbs the regularity of form of the 

 mesenteries and stomocheum. 



As noticed by Krenipf, the modification occurs in oidy a 

 limited number of the many poly[)s making up a colony; the 



* There is possibly some confusion as regards the terms dorsal and 

 Yi-ntral. Krenipf states that the media;) organ in J'ucino/wra occurs 

 within the ventral directive chaniher, whereas in the Hawaiian specimens 

 il is ilontal. 



