NATURAL HISTORY SOCIETY OF GLASGOW. 31 



with in the neighbourhood of Dunbar, by Mr. James Bennie, with 

 small bodies attached to them in various stages of development, 

 which proved on investigation to be a neAv form of Productus. 

 In the younger conditions attachment took place by the spines 

 of the ventral valve clasping the object to which the brachiopod 

 adhered, but as development progressed the whole surface of the 

 valve became united to the Crinoid stem. Had matters remained 

 in this state, all well and good, we should merely have had a species 

 of a genus not hitherto supposed to be adherent showing signs of 

 it. " Attachment took place during the life of the Crinoid; for in 

 nearly every case where the Productus remains adhering, we find 

 that its rate of growth was less than that of the Crinoid, the result 

 being that the substance of the latter surrounded or enclosed its 

 parasite, first the encircling spines disappearing and gradually the 

 shell. "We have specimens showing this remarkably well in all 

 stages of the process, from the mere absorption of the spines by the 

 substance of the Crinoid, up to the total disappearance of the 

 Productus itself, when the Crinoid stem assumes a swollen or dis- 

 torted appearance."* In my paper on this subject, and from which 

 the above extract is taken, I gave a figure f of a Crinoid stem com- 

 pletely surrounded by the grooves caused by the tightening spines, 

 and which will afford some idea of the irritation which must have 

 been set up in the Crinoid stem by their unwelcome presence. P. 

 complectens is perhaps one of the best examples of the cause of en- 

 largement in the columns of Crinoids, because, from the exceptional 

 advantage of possessing many individuals, it has been possible to 

 trace onwards and prove the process from the earliest stage to the 

 point where we have presented to us only a swollen and distorted stem. 



The foregoing examples may be taken as illustrating the manner 

 in which the enlargement of Crinoid stems is produced by the ex- 

 ternal attachment of extraneous bodies, which afterwards become 

 internal through the rapid and extra secretion of Crinoidal sub- 

 stance around them. 



We have now to examine a different set of agents occupied in 

 this process, those which, working from the exterior, penetrate the 

 stem, and there, setting up local irritation, probably cause an un- 

 usual secretion of the substance of the stem, giving rise to the 

 swollen or enlarged appearance. 



*Loc. cit., p. 460. tT. 34, f. 12. 



