10 Mr. H. M. BernarJ on the 



which it lias disappeared from view or is difficult to unravel. 

 Only in the few Madreporids (the chief families of the 

 Perforata) above mentioned can it be said to have been aborted, 

 and then only in a limited sense, for the whole coral skeleton 

 is its product. If the original rim of the cup is replaced as 

 the edge of the theca by new thecse formed either by the 

 rising up of concentric folds from its floor or of radial plates 

 from irs sides, or by complicated combinations of these two, 

 these new thecse are strictly infoldings of the prototheca. 

 The prototheca, then, however obscured its early cup shape, 

 being replaced by secondary cups produced by its own 

 infoldings, remains throughout the fundamental element in 

 the Mudreporarian skeleton. 



I propose here to trace some of the more obvious trans- 

 formations of the prototheca, treating them entirely morpho- 

 logically — that is, simply as forms which admit of explanation 

 and deduction from simpler forms, and without regard to their 

 real phylogenetic sequences. 



The working out of these latter — that is, the attempt to 

 discover the real places of these transformatory processes in 

 the genealogy of the Madreporaria — must be a work of time. 

 I am convinced, however, that it will at once give a new and 

 much needed interest to the student of the stony corals. 



We relurn, then, to our simplest form (diagram fig. 1). It 

 shows us a conical cup standing on a flattened slightly ex- 

 panded base and gradually thickening upwards. The problem 

 cf increasing instabiliti/ must obviously have been one of the 

 first which the polyp inhabiting such a skeleton had to solve. 

 1 shall endeavour to show that the earliest divisions of the 

 Madreporaria were due to the different ways in which this 

 problem was solved. 



I. Falling over and recovery of the upright position. — The 

 simplest of all methods was to fall over so that the flesh of 

 the polyp could come once more into contact with the sub- 

 stratum and secrete a new cementing layer where it touched. 

 From this new base the polyp could bend upwards once more 

 securely attached. The following is some of the evidence 

 which shows that this actually took place : — 



{a) The earliest period is specially characterized by the 

 great number of single corals which are conical but curved. 

 The curve is exactly what is required ; that Is, it is most pro- 

 nounced at the tip, e. g. Zaphrentis, Menophyllum, &c. 



{b) All these curved corals have what is known as a fossula, 

 that is a deep depression within the calicle and most frequently 

 on the convex or what is called the " dorsal " side. The 

 fossula has a very simple explanation, if the assumption of 



