OOTINEON LTNDAHLI. 465 



similar condition holding also in the Zoanthese ; presumably, 

 therefore, the secretion of (?) raesogloea for the adhesion of the 

 sand is effected by wandering cells from the endoderm, but I 

 have not been able to detect their presence. 



When stripped of the incrusting sand the animal has the 

 appearance represented in fig. 2 ; the surface of the mesogloea 

 is pitted by impressions of the sandy particles, and lines indica- 

 tive of the mesenteries radiate towards the central cone. The 

 external body-wall thus exposed consists of a thick mesogloea, 

 lined internally by a cubical endoderm, and is provided 

 with a single layer of endodermal circular muscle-fibres. This 

 description applies also to that part of the column which is 

 turned inwards and downwards in retraction, but must be ex- 

 tended by the fact that there is a profusion of " mesodermal " 

 circular fibres in this region, intermingled with a few longi- 

 tudinal fibres which are doubtless used in expansion; the 

 mesogloea is extremely thick. Just before this inturned part 

 passes into the oral disc the sand particles are no longer 

 adherent, the ectoderm is met with for the first time, and, like 

 the mesogloea below it, is thrown into six folds or ridges 

 (fig. 13). 



The oral disc is, in complete retraction, pulled outwards and 

 downwards into pockets which contain the tentacles, as is so 

 frequently the case in Actiniaria and Madreporaria, this with- 

 drawal being effected by the mesenteries. I have not been 

 able to assure myself of the exact number of the tentacles 

 either by sections or dissections. In addition to the difficulties 

 of investigation already mentioned, the exact anatomical 

 relations are often very hard to make out, because, owing to 

 the great vertical length of inturned body-wall plus oral disc 

 plus stomodseura, the two latter are generally bent round in 

 a J- shape in most cases (fig. 7), rendering the interpretation of 

 sections troublesome. So far as I can make out (and I infer 

 that Carpenter and Moseley were of the same opinion) there 

 are twelve tentacles, arranged as is shown in fig. 9, with the 

 addition of a twelfth tentacle on the left of the upper directive 

 mesenteries. This would amount to an entocoelic tentacle 



