12 Echinodermata. 



The interior of the actinal part of the test is marked by 5 radial and 1 inter- 

 radial ridges which start from the perignathic girdle. 



Ooderlein points out that in the recent Goniocidaris clypeata from Japan the spi- 

 nes round the apical area have shieldlike ends , and correspond very closely to 

 the radicles of Cidaris Buchi from the St Cassian beds. They may possibly serve 

 to enclose a marsupium, as this species is viviparous. 



VI. Holothurioidea, 



See also Howell, supra, p 3. 



Vogt & Yung give a detailed description of the anatomy of Cucumaria. The 

 mucous cells of Semper and Jourdan are parasitic in nature. The terminal 

 vesicles of the lungs are completely closed and do not communicate with the 

 coelom. The mesentery between the point of union of the genital tubes and the 

 origin of the oesophagus supports a problematic canal , closed at both ends and 

 lined with cells which contain granular matter. The intestinal vascular system 

 is purely lacunar in character and is in manifest communication with the water- 

 vascular system. The collecting vessel in relation with the ventral vessel of the 

 gut is comparable to Perrier's collateral vessel in the Urchins. 



Ludwig describes the anatomy of 5 six- rayed individuals of Cucumaria 

 Planci, and concludes from the relations of the mesentery, lungs, and water-tube 

 (stone -canal) that the sixth ray is intercalated between the 2 of the bivium, 

 usually on the left, but sometimes on the right of the median Interradius. 



Lamport states that the viviparous Cucumaria crocea has 2 closed marsupial 

 pouches situated on the ventral side rather behind the middle of the body. They 

 appear to have been formed by invagination of the body wall as they contain 

 similar calcareous bodies ; but no connection can be traced between them and the 

 genital glands , and it is not clear how the embryos reach the dorsal ambulacrum 

 where they were found by Wyville Thomson as quoted by Theel ( 1 ). Levinsen 

 finds that Cucumaria minuta (Fabr.) is viviparous. The young develope in 2 elon- 

 gately oval sacs which are situated anteriorly and open externally within the tri- 

 vium. There is no apparent connection between them and the genital glands. 



Theel f 1 ) thinks that the common ancestors of the Holothurians were Cucu- 

 man'a-shaped forms, furnished with an open stone-canal , feet, and a well-deve- 

 loped ambulacral system. The apodous condition is not the primitive one, but is 

 due to reduction, which is still going on in the Molpadidae. 



Theel ( 2 ) mentions specimens of Echinocucumis typica which have an almost com- 

 pletely spherical body with a highly reduced bivium , so that the mouth and anus 

 are closely approximated. 



