REPORT ON THE AXTTPATHARIA. 65 



In such forms as Pteropathes Jragilis the coenenchyma is confined to the back of 

 each branch, the zooids on the anterior surface being so closely packed together that 

 there is no room for interzooidal tissue. In other cases where the polyps are more 

 isolated, the connections between the polyps on the anterior surface of each branch 

 contain prolongations of their ccelentera. Mesoglceal septa usually occur, which 

 incompletely separate the individuals from one another. 



Skeleton Formation. 



The axial skeleton in all Antipathidse consists of thin concentric horny lamellaa 

 arranged around an axial lumen, which is usually central in position. AVhen a number 

 of layers are superimposed the colour is usually dark brown or black ; in thinner 

 portions of the corallum the colour is golden brown. In a number of species the older 

 portions of the corallum become covered with a glossy varnish-like substance, which 

 is sometimes so thick as to cover all but the apices of the spines. The lumen of the 

 axis appears to be divided by thin irregular partitions into a number of small chambers. 

 The sclerenchyma is surrounded by a more or less complete layer of flattened cells, which 

 G. v. Koch terms the axis epithelium. This is surrounded by a mesogloeal sheath, and 

 the whole is clothed with entoderm. The mesogjlcea of the sheath is connected with that 

 of the coenenchyma by means of a short longitudinal septum running the whole length 

 of a branch. V. Koch suggests that the axis epithelium, which evidently secretes the 

 sclerenchyma, has an epiblastic origin. In this case the axis epithelium is comparable 

 with the ealijcoblasts of V. Heider, which secrete the calcareous skeleton in Madre- 

 poraria. I have not yet fully studied this point, but so far as my observations go they 

 appear to support v. Koch's view. In Schizo2Xtthes crassa transverse sections of the 

 apex of a branch show an involution of the ectoderm which is continuous with the 

 mesoglcea adjoining the mesogloeal sheath of the sclerenchyma, but I have not yet traced 

 the lumen from the invagination to the interior of the sheath. Further details must be 

 deferred until I have made a more complete investigation of the material in hand. 



Origin and Arrangement of Spines. 



Pourtales was the first to lay stress on the form and arrangement of the spines 

 which are present on the axis of all Antipatharia, with the exception of Savaglia 

 lamarcki. He thought them to present such manifold variations in shape and arrange- 

 ment as to offer valuable characters for specific purposes. Although perhaps the 

 spines do not afford absolutely reliable characters, it nevertheless appears probable 

 that there is a " typical " arrangement in certain portions of the corallum which 

 is constant in each species. It may be added further, that the typical arrangement 



(ZOOL. CHALL. EXP. — PART LXXX. — 1SS9.) Llll 9 



