Morphology o/Antedon rosacea. 



37 



space on the dorsal side of the central capsule which is marked 

 /' in fig. 267, and c in fig. 276, and is described in the expla- 

 nation of tlie former figure as one of these cavities of the cham- 

 bered organ, is nothing wliatever but a rent in the organic basis 

 of the floor of tlie centro-dorsal piece. These rents often appear 

 in the skeletal tissues when very thin sections are cut, and I 

 have been familiar with them for years; but I have many 

 sections through the calyx, both of Antedon rosacea and of 

 other species of Comatulaj, in which there is no trace of them. 

 Tliree such undamaged sections are figured in my Actmometra- 

 memoir* ; and I certainly never expected to find an accidental 

 fracture in the skeletal tissue outside the central capsule de- 

 scribed as a part of the chambered organ, the cavities of which 

 are entirely 7vitlun this capsule, as explained above. If there 

 really be such a diverticulum of the body-cavity within the 

 calcareous substance of the centro-dorsal piece, as described 

 by Vogt and Yung, i. e. between its inner floor on which the 

 central capsule rests and its external surface, its presence could 

 easily be demonstrated by rubbing away the outer surface of 

 the centro-dorsal until this cavity was reached ; and I com- 

 mend this method of proving the accuracy of their anatomical 

 descriptions to the attention of Messrs. Vogt and Yung. 



It would be well also if they would use the same method 

 to demonstrate the existence of the " cavite de la syzygie," 

 which they represent in fig. 279 on p. 558. They describe 

 this section as a " coupe transversale d'un bras, frisant une 

 syzygie ;" but in reality it 

 is very considerably ob- 

 lique, and so far as its 

 dorsal portion is concerned 

 would be classed as a bad 

 section, owing to the large 

 amount of skeletal tissue 

 which has been torn away 

 by the knife. It will be 

 apparent from the annexed 

 figure (C) that the plane of 

 each syzygial face is abso- 

 lutely transverse to the axis 

 of the arm, so that a truly 

 transverse section would 

 pass through all the ridges 

 radiating outwards from the central canal and show no trace ot 

 the paired muscular bundles or else show no ridges at all. But 



* Traus. Linn. Soc. Lond. 2nd ser. (Zool.), vol. ii. 1879, pi. viii. figs. 3, 

 4,7. 



Syzygies in the arm of Antedon rosacea. 

 A, the epizygal; B, the hypozygal ; 

 C, dorsal view of au arai-fragment. 



