NATURAL HISTORY SOCIETY OF GLASGOW. 337 



3. Diastopora megastoma. — Thirty specimens were examined. 

 The fabricators of this structure follow those of ArchaeojJora in their 

 style and manner of work, although less deftly finished, and like- 

 wise in selecting small stems, not worn or tarnished, on which to 

 squat. They seem, too, to have constructed their characteristic 

 fabric when the crinoid was in the erect position, — including in 

 the web short broken branches, which are seen or indicated by 

 irregularity of surface, — and also of encircling the crinoids without 

 passing on or over the ends of the stems — hence, probably, when 

 alive. The substance or mass of the organism is from two to six 

 times thicker than the more delicate and ornate Archaeojpora. Of 

 the thirty specimens examined it has been found that twenty 

 encircle the stems, thus: eleven on Rhoclocrinus, seven on 

 Poteriocrimis, and two on AcUnocrinus. Nine, which do not 

 encircle completely, consist of seven of Poteriocrinus, and two 

 of a species of Bhodocrinus. 



It would thus appear that Stenopora tumida had been constructed 

 in clusters, almost exclusively on large and dead stems, and their 

 form and limits suggest the idea that these stems must have been 

 partially sunk in the mud. It is equally apparent that Archaeopora 

 had been constructed on small, erect, perhaps living stems and 

 branches, conditions which equally apply to Diastopora. 



Now the primary object of this examination was a search for 

 evidence of a repelling agency, or of a defensive or protective force 

 exercised by crinoids infested by irritating parasites. One would 

 naturally conclude in the case of the two last-mentioned species, 

 that if any resistance had been made in any form to the 

 progressive course of the aggressive action, it would have been 

 found in connection with these encircling polyzoa. Nothing of 

 the kind has been observed. But, where least expected, it has 

 been found that a fragment of Adinocrinus has attached to it a 

 fine specimen of Stenopora tumida, which, after construction, seems 

 to have repressed or hindered the growth of the crinoid, so far 

 as the cluster extended, while beyond the edges of that cluster the 

 stem is enlarged, giving the specimen the appearance of being 

 slightly sunk in the stem, or what amounts to the same thing, the 

 stem is raised or bulged above the level of the invading body, and 

 presents throughout a corresponding general enlarged and healthy 

 condition. Such an operation is undoubtedly the result of life- 

 action; but there is no evidence that this action was, in the 



