NOTES ON ECHINODERM MORPHOLOGY. 13 



of the chambered organ and the lower part of the glandular 

 structure arising from it. In fact it is the absence of relation- 

 ship to internal organs which markedly distinguishes the 

 plates in the apical system of Ophiurids and Asterids from 

 their homologues in Urchins and Crinoids. In the former 

 group the basals are frequently pierced by the genital ducts 

 and the radials (oculars) pierced by the water vessels. In the 

 Crinoids, however, the chambered organ (which is so important 

 a part both of the vascular and of the nervous systems) is 

 lodged in a cavity bounded by the basals and radials; while the 

 lower part of the plexiform gland arising out of it passes 

 upwards within the radial funnel. The primary cords proceed- 

 ing from the chambered organ pierce the basals ; and the 

 secondary cords resulting from their bifurcation enter the 

 radials, where they are connected by the circular commissure 

 and then pass on to the arms. 



Some palaeontologists have asserted that the basal plates are 

 absent in the Eugeniacrinidae and Holopodidae. thereby 

 suggesting very considerable morphological difficulties, as I 

 have pointed out elsewhere ji and I have yet to become 

 acquainted with a Crinoid in which the existence of basals 

 though perhaps not actually demonstrable, cannot be deduced 

 from the analogies presented by the calyx to that of 

 Rhizocrinus lofotensis, Bathycrinus carpeuteri, and 

 other forms in which the interbasal sutures disappear when 

 maturity is reached. 



A parallel condition to the variations in development and 

 functional unimportance of the plates in the apical svstem of 

 the Stellerids is presented by the oral system of certain 

 Palseocrinoids, e.g. the Platycrinidae, Actinocrinidae 

 and Rhodocrinidae. In these families a regular "calyx" 

 is developed around the left larval antimer, like that which 

 appears on the right antimer of all Pelmatozoa and Echinozoa. 

 In the Neocrinoids, as in the Ophiurids and in the Psolidae 

 among Holothurians, five " oral " plates are developed around 



^ " On the Supposed Absence of Basals in the Eugeniacrinidse, and in certain 

 other Neocrinoidea," ' Ann. and Mag. Nat. Hist.,' May, 1S83, pp. 327—334. 



