Professor Yakovlev — On Rugose Corals. 109 



Referring to the colonial Rugosa, I have explained how the 

 characteristic forms of the colonies are correlated with the mode of 

 multiplication, and demonstrated the part played by these corals in 

 reef-building. Here and there I have pointed oqt differences between 

 the Rugosa and the Hexacoralla, which do not admit the former to 

 be considered as the progenitors of the latter, though this is probably 

 claimed by the majority of palaeontologists and zoologists. 



This examination (pursued by me for many years) of the form and 

 functions of the Rugose Corals and of the questions they raise, I now 

 look upon as sufficiently complete to render desirable a review of the 

 results of my work, wbich throws fresh light on the Rugosa as well 

 as providing a causal explanation of the origin of the peculiarities of 

 this specialized group. In conformity with the character of the 

 present paper, the exposition will be given concisely, without 

 citations and references, without criticism of other authors, without 

 any details ; those who are interested will find all this in my 

 previous publications. 



The shape of the Rugose polyparium is considered to be typically 

 conical. Herein the Rugosa differ from the Hexacoralla, which 

 mostly have a cylindrical polyparium ; and this difference of body- 

 form may be seen in the soft-bodied Actiniae now living. The 

 Rugosa are first found in Silurian rocks, but doubtless existed 

 previous to this, and before Silurian times the Rugose polyparium 

 had already departed from the fundamental simply-conical shape. 

 It had acquired, near its proximal end, a lateral attachment to the 

 substratum, unlike the basal attachment of the Hexacoralla (see 

 PL VIII, Pigs. 1-4). This lateral attachment ioas correlated with their 

 life in epicontinental seas. The basal attachment of the cylindrical 

 (or, in rare cases, conical) polyparium of the Hexacoralla living in 

 deeper, calm water, as much satisfies the requirements of solidity as 

 the lateral attachment of the Rugose conical polyparium living in 

 a zone of the sea characterized by comparatively rough or at least 

 agitated water. 



The lateral attachment, then, of the Rugose polyparium is an adapta- 

 tion to definite environmental conditions. It has modified the original 

 form of the simply -conical polyparium and has imposed upon it a definite 

 orientation correlated with the direction of the prevailing currents. Por 

 a conical polyparium lying on one side on the sea-bottom must of 

 necessity turn away its mouth from the mud of the sea-bottom in 

 order to avoid suffocation. Thus the simple cone with a straight axis 

 becomes one with its axis curved in one plane — a form resembling 

 the horn of an ox, and suggesting such trivial names as cornu, 

 corniculum, cornucopia, cornu-bovis, ceratites, buceros, etc. Moreover, 

 all the individuals of one locality were orientated in the same 

 direction, namely, with their convex sides towards the direction of 

 the prevailing current (see Text-fig. 1). Only thus will a polyparium 

 of such a shape offer the maximum resistance to wave- and current- 

 action tending to tear it from the substratum. 



Now the scar formed by the attachment of the polyparium to the 

 substratum as well as the root-like processes serving the same 

 purpose necessarily occur as a rule on the convex side of the corallum. 



