NATURAL HISTORY SOCIETY OF GLASGOW. 33 



example of this which has come under my notice the enlargement 

 of the stem was simply confined immediately to the part in 

 question, and did not extend to a general swelling of the stem; 

 neither was there any aperture. Miller was so far correct in his 

 general description of this phenomenon of enlargement; only his 

 remarks apply not to the loss of a side-arm, as he supposed, but to 

 the causes which follow. 



Second. — The combined researches of Mr. Rofe, a "Corresponding 

 Member,'' and myself, haYe proved that another cause is the 

 external attachment of extraneous bodies, such as corals, stems 

 of smaller Crinoids, certain Polyzoa, and a species of Prodv.ctus. 

 Future research will probably disclose other agents. 



Third. — Enlargement is certainly caused by the attack of para- 

 sites, although the cause and effect under this heading are not 

 so clear as they might be. There is some reason to believe, 

 judging from PI. I. tigs. 18 and 19, that an Annelide was one of 

 these. 



In seeking a cause for this peculiar enlargement of Crinoidal 

 stems, attention must be given to the theory of disease advanced 

 by a " Corresponding Member;" but I think, after due consideration 

 of the numerous facts I have now brought forward, the theory of 

 disease, pure and simple, will have to be relegated to the position 

 of one of the minor causes. After all, no doubt, any form of 

 enlargement may be said to a certain extent to be disease, because 

 it arises from an unnatural and undesirable state of the Crinoid, 

 viz., the adherence of extraneous bodies during growth, or the 

 attack of burrowing organisms within. 



That these causes should give rise to serious disorganisation on 

 the part of the Crinoid is not to be wondered at, when we take 

 into consideration the important and delicate part played in its 

 economy by the vascular axis contained in the columnar canal.* 

 Any obstruction to the growth of the column and its axis would 

 probably call forth all the resistance the Crinoid was capable of, 

 and its chief endeavours would be to either get rid of the intruder, 

 or, by the more vigorous deposition of matter round about the part 

 attacked to render the life of its antagonist untenable. 



* On this head, see P. H. Carpenter, on some points in the Anatomy of 

 Ptntacrinus and Ehizocrlnus {Jour. Anat. and Phijs., 1877, XII., pt. 1, pp. 

 35-53.) 



VOL. IV. C 



