.Oi'G Miscellaneous. 



has converted into a tunnel and buried in the depths of the body 

 of the thus transformed polype. The following are the facts which 

 have led me to these conclusions. 



The determination of the analogies which exist between the 

 tissue of the vohirainous endudermic enlargements of Madrepora 

 and that of the organ of wliich I have established the homology 

 with a tentacle in certain Oculininte * — analogies which bear not 

 only on the structure of the cellular elements, but also on the very 

 special histocliemical reactions of their contents — has from tlie very 

 outset prepared me to understand tlie following anatomical con- 

 ditions : — 1. The tentacles, so well developed and so easy to observe 

 even when contracted, in normal individuals, are comi)letelv wanting, 

 at^ least in their usual form, on the buccal disc of modified individuals, 

 which thus appear to be devoid of them. 2. The pharynx of these 

 latter, characterized by its very diminutive length, its narrowness, its 

 differentiated ectoderm, is not to be confounded with the irregularly 

 ])leated wide and long funnel which precedes it and on the vertical 

 or oblique Avails of which the two orifices of six U-shaped canals 

 open. This funnel is, in effect, nothing more than the invaginated 

 1)uccal disc of the polype, and, as is known, deprived of visible 

 tentacles. The orifices of each of the canals are therefore not situate 

 in the pharynx, but, and the relation is of capital importance, on the 

 surface of the buccal disc : they are arranged along one of its radii, 

 one in the neighbourhood of the mouth, the other on the marginal 

 border. 3. I have been able to observe an individual which 

 ])iesented only one U-shaped canal-organ, that of one of the left 

 directing partitions ; all its other partitions were normal. 



The animal was adult, provided with six endocceles and six ecto- 

 cceles, and should have possessed twelve tentacles. An examination 

 of its buccal disc shows {a) that it had but ten ; {h) that the two 

 vacant places, very clearly marked in the crown of tentacles and 

 representing the two missing elements, corresponded precisely, ono 

 Avith the directive endocoele, of which the left mesentery was tho 

 only one modified, the other with its left ectocoele. 



Collating these facts, one may deduce from them particularly : — 



1. That there is a constant correlation between the presence of 

 the U-shaped canal-organ in an individual and the apparent absence 

 of tentacles on its buccal disc. 



2. That the correlation is particularly manifest in the very clear 

 case in which only a single organ is found in the individual, the 

 case in which the two missing tentacles are those of the endocoele 

 and ectocoele which it occupies, 



3. That the plane in which the U-shaped canal with its two 

 orifices is contained coincides with the i)lane of separation of two 

 neighbouring tentacles. 



I am now in a position to demonstrate how the transformations 

 which give rise to the arrangement under consideration in certain 



* Seriaptora, Stylophora, Poscilopora : it is the dorsal tentacle which, 

 iu these three genera, is modified, and not the ventral as I am made to 

 sav by an error in the text of mv note (' T'oniptes Ixendus," J8th Mav, 

 10(.)3). 



