ENDOSKELETON. ANIMALS. 9 



(ccelenteric canals). The surface of the organism is alone 

 living, the lower deserted portion of the tubes being cut off 

 by tabulae. PI. ill. fig. 1. 



Presented by Dr. H. Woodward. 

 Moseley, Phil. Trans., vol. clxvi. 1877, p. 91. 



A. 25. Perforate corallum of a Madrepore (Madrepora muricata). 

 The corallum is permeated by a network of coalenteric 

 canals, so that all except the oldest portions may be regarded 

 as living. The ectodermic cells (calycoblasts) in contact 

 with the external surface of the corallum effect its increase, 

 but they more or less disappear from the deeper parts. 

 PI. ill. fig. 2. 



Fowler, Q. J. Micr. Sci., vol. xxvii. 1887, p. 1. 



Ogilvie, Phil. Trans., vol. clxxxvii. 1896, p. 83. 



A. 26. Horny corallum of Black Coral (Antipathes ulex). This 

 material is tougher and less rigid than that of the preceding 

 specimens. 



Skeleton consisting in part or entirely of separate sclent es (spicules). 

 Each spicule is formed in an ectodermic cell that has migrated 

 into the mesoglcea (firm jelly-like substance between ectoderm 

 and endoderm } formed by the ectoderm). 



A. 27. Spongodes florida, a colonial Alcyonarian. Some of the 

 supporting spicules are shown, detached, by the side of a 

 drawing of their microscopic appearance. 



A. 28. Two specimens, and diagram of the structure of an Organ- 

 pipe Coral (Tubipora musica, Order Alcyonaria). The tubes 

 and platforms that unite them are formed by fused spicules, 

 the spicules in the polyp-walls remaining separate. Coelen- 

 teric canals running in the platforms unite the polyps. A 

 small inner tube is often formed as the result of the detach- 

 ment and shrinkage of the soft tissues that line the outer 

 large tube. PI. IV. fig. 1. Presented by Prof. C. Stewart. 

 Hickson, Q. J. Micros. Sci., vol. xxiii. 1883, p. 558. 



