Anatomy, Physiology, Embryology. II. Pelmatozoa. 



187 



The oral or actinal system forming the vault of Actinocrinns was developed on 

 the left larval antimer in exactly the same way as the abactinal system of the 

 calyx was developed on the right antimer ; but in the Neocrinoids it is reduced to 

 the five oral plates. Some Palaeocrinoids, however, e. g. the Ichthyocrinidae, 

 seem to have had an exposed disc such as occurs in the recent forms, though 

 always retaining a subtegminal mouth, with the possible exception of Cocco- 

 crinus. The more or less divergent views of Wachsmuth & Springer, Loven, 

 Perrier and Ludwig, respecting the above homologies, are discussed at length. 



Perrier ( 5 ) finds that the so called intestinal vessels of Comatula commence 

 as fibrocellular cords which only acquire a lumen at the end of the Pentacrinoid 

 stage. Extensions of them traverse the body-wall and open externally by the ciliated 

 waterpores. The spongy organ, which also communicates with the exterior, is 

 formed out of the water-tubes round the gullet ; and the peripheral cavities of the 

 chambered organ are dilatations of five principal vessels which contribute to form 

 the vascular envelope of the dorsal organ. Its axis is formed from a fold of the 

 right peritoneal sac and consists of the genital stolon which ramifies above 

 the mesentery into the arms and pinnules, but only its distal portions become fer- 

 tile. In Comatulae as in Urchins the so called vascular system communicates with 

 the ambulacral canals. 



Perrier ( 4 , 6 ) further gives a connected resume of his various communications 

 on the anatomy and development of Comatula (Bericht for 1883 I p 128 and 

 1884 I p 173). The first water-tube is continuous with a water-pore and does 

 not open directly into the coelom as stated by Ludwig ; and the water-pores of the 

 adult open into a system of vessels beneath the perisome, or into the water-tubes, 

 some of them forming the labial plexus. The water-vessels and supposed blood- 

 vessels are in reality only parts, together with the coelom, of one complex system 



