REPORT ON THE CRINOIDEA. 127 



these plates. It appears to me verj'- probable that this may also be the case iu 

 Thaumatocrinus (PL LVI. figs. 1-4), i.e., that the primary cords pass right up out of the 

 basals into the interradials and then divide, so that the secondary corc^s would enter the 

 sides of the radials as in Bathycrinus, instead oftheir inner ends as in Pentacrinus and 

 Comatula. 



G. The Sacctjli, and the Colouring Matters. 



The nature and functions of the sacculi are as much a puzzle to me now as they were 

 when I first began to study the Criuoids in 1875 ; and I have nothing to add to the 

 observations of Wyville Thomson and Perrier on their appearance in the li\ing animal, 

 both larval and adult. Colourless during life, they become strongly tinged after death 

 by the pigment set free from the perisome. Their occurrence in the wall of the digestive 

 tube in Antedon rosacea was first noticed by Ludwig ; and I have found them in the 

 very lowest part of the cup of a larva with five cirrus-stumps, just above the chambered 

 organ. But this is the only species known to me which presents this peculiarity. In all 

 other types in which the sacculi occur at all, they are invariably limited to the immediate 

 neighbourhood of the water-vessels. Abundant in most species of Antedon, they 

 never occur in Actinometra, and I suspect that Ludwig's reference to their presence in 

 this genus is due to an oversight.^ At any rate I have not been able to find them in 

 Actinometra trachygaster and Actinometra bennetti, the two species w^hich had come 

 under his observation. 



They vary considerably in distribution among the other genera of Comatula. I 

 have not succeeded in finding them in Thaumatocrinus, while they are but scantily 

 developed in the three species of Atelecrinus. Eudiocrinus indivisus and Eudiocrinus 

 atlanticus have them in al)undance ; while there are few in Eudiocrinus varians and none 

 in Eudiocrinus semperi or in Eudiocrinus japonicus, so far as I have been able to make 

 out. Promachocrinus kerguelensis has them on the pinnules, but they are very scanty or 

 absent elsewhere. Neither have I found any in a small series of sections through a 

 Holopus-arm ; and though structures of the same nature occur sparingly in Pentacrinus, 

 Rhizocrinus, and Bathycrinus, they are but poorly developed and irregular in their 

 occurrence. 



In some species of Actinometra individual vesicular bodies resembliDg the elements of 

 the sacculi are scattered through the ventral perisome ; but there is no regular arrange- 

 ment of them into groups at the sides of the ambulacra as in the endocyclic Crinoids. 

 When the ambulacra are plated, as in many tropical Antedons, the sacculi are lodged 

 between the successive side plates, the front edges of which are notched for their reception 

 (PL LIY. figs. 4, 6-9) ; while they occupy little pits in the large plates which cover the 



1 Zeitschr. f. xviss. Zool, BJ. xxix., 1877, p. 59. 



