REPORT ON THE CRINOIDEA. 135 
the last (Station 214, off Meangis Islands) the principal hosts were <Antedon 
angusticalyx and Pentacrinus alternicirrus, 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 Pl. XXVII. figs. 7, 8, in the former of which the edge of the parasite is just 
visible at the opening of the cyst. This cyst is principally formed round a pinnule; but 
the same kind of thing is sometimes formed in the substance of the arm itself, as shown 
in Pl. XXVIL. figs. 9 and 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 paleontologists. Rofe 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. R. 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 growth seem to be very common in the stems of Apiocrinus 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 Paleeocrinoids. 
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 of Pentacrinus alternicirrus (Pl. XXVII. figs. 7-10), 
2.e., eystiform 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 Comatule and of 
Pentacrinide. 
1 Note on the Cause and Nature of the Enlargement 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, pls. i, ii. 
3 Swiss Crinoids, pl. xi. figs. 18, 36-38. French Jurassic Crinoids, pl. 65, figs. 4-6, 8 ; pl. 80, figs. 2, 2a, 13 ; pl. 99, 
figs. 5a, 5b, 5d. 
