EEPORT ON THE CRINOIDEA. 135 



the last (Station 214, off Meangis Islands) the principal hosts were Antedon 

 angusticalyx and Pentacrinus alter nicirr us, several examples of the latter being 

 remarkable for the number of cysts on their arms. Two views of one of these cysts are 

 shown in PI. XXVII. figs. 7, 8, in the former of which the edge of the parasite is just 

 visible at the opening of the cj^st. This cyst is principally formed round a jiinnule; but 

 the same kind of thing is sometimes formed in the substance of the arm itself, as shown 

 in PI. XXVII. figs. 9 aud 10, the inhabitant of the cyst being again visible through its 

 mouth. 



Thus then, while Stylifer bores holes into the calyx of a Crinoid, Myzostoma produces 

 swellings and inequalities of growth in the arms and pinnules. I have never met with 

 any distortion of the stem which could be considered as resulting from the action of a 

 parasite ; and it is therefore curious that abnormal growths in the stems of fossil Crinoids 

 should have attracted the attention of so many palaeontologists. Eofe showed, for 

 example, that one cause of the enlargement of the stems of Carboniferous Crinoids arose 

 from the attachment of a parasitic coral, and the subsequent endeavours of the Crinoid to 

 envelop the latter by an undue secretion of calcareous matter.' It has also been shown 

 by Mr. E. Etheridge, jun.,'^ that a similar distortion may be due to the adherence of 

 certain Brachiopods (Productus or Chonetes). These grew less quickly than their hosts, 

 and so became gradually surrounded and enveloped by the calcareous deposit secreted by 

 the latter. The attachment of Polyzoa, again, may also give rise to enlargement, and 

 even the accidental approximation of the stems of two individuals seems to have 

 sometimes resulted in a complete but irregular union between them. Enlargement and 

 irregularities of growi;h seem to be very common in the stems of Ainocrinus and 

 Millericrinus, though not in Pentacrinus ; and they have often been regarded as the 

 results of injury. But their exact nature and causes have not yet been determined as 

 satisfactorily as in the case of the Palteocrinoids. 



There are, however, some stems of Millericrinus figured by de Loriol,^ from the 

 Jurassic rocks of France and Switzerland, which present characters of the same nature as 

 those shown on the arms and pinnules oi Pentacrinus alternicirrus (PL XXVII. figs. 7-10), 

 i.e., cystiform enlargements, each with an external opening. Both Prof. L. von Graff 

 and myself are inclined to regard these as due to the action of Myzostomida or of similar 

 parasites. But it is singular that they should be developed on the stem ; for I have 

 never found a Myzostoma-cyst on the stem of any recent Crinoid, though at some 

 Stations (170, 214) they were abundant upon the arms, both of Comatulse and of 

 Pentacrinidse. 



1 Note on the Cause and Nature of the Enlarf^ement of some Crinoidal Columns, Geol. Mag., vol. vi. p. 351. 



2 Observations on the Swollen Condition of Carboniferous Crinoid Stems, Proc. Nat. Hist. Soc, Glasgow, vol. iv., 

 1879, pp. 19-36, pis. i., ii. 



3 Swiss Crinoids, pi. xi. figs. 18, 36-38. French Jurassic Crinoids, pi. 65, figs. 4-6, 8 ; pi. 80, figs. 2, 2a, 13 ; pi. 99, 

 figs. 5a, 55, 5d. 



