76 S. LOVEN, ON POURTALESIA, A GENUS OF ECHINOIDEA. 



of the regenerative energy of these long siippressed parts, and, in obedience to the 

 predorainant tendency of abdominal growth, prcpared tlie recession, b}'' the way thus 

 laid open, of the perforating agency of the madreporitic tubuli. Accorapanied by correl- 

 ative changes in other parts; transinitted, Avith tendencies enforced, from generation 

 to generation, frorn embryo to embryo, and resuraing innumerable times its plastic 

 work, this evolutional process, siraultaneously operating in a number of individuals, always 

 at an early stage never found fossil, resulted in the location of the madreporite in the 

 restored costal 5 of the adult. Then a period of rest followed in the calycinal system, 

 during which innumerable specimens were preserved recording the transformation, 

 whicli thus may seem to have been accomplished in a relatively short space of geologi- 



cal time, and, as it now appears to us, suddenly. The seas of 

 the present era harbour at least one transitional form, the an- 

 tique looking Genicopatagus aflinis Al. Ag., in Avhich the cen- 

 tral disk and the costal 5 are reinstated, separating the I and V, 

 and preparing the way for the madreporite, which still how- 

 ever remains in the aporous costal 2. It is an abyssal form, 

 and such are probably all the recent Ethmophracti, "while the 

 Ethmolysii, which have but few representatives in the great depths, 

 Genicopatag^affinis^L. Ag., ^rc llttoral auimals ^ccz' £|o/»jV. It is among these that the mad- 

 Caiycinai System. rcporlte, aftcr a period of rest, in our days seems to show 



signs of once more moving, and of transgressing its latest line of demarcation. 



Further research, extending över a large number of specimens of these and other 

 species, from difierent localities, will decide whether there be valid reasons for regard- 

 ing this regression of the filtering apparatus beyond its old boundary as an evolutional 

 stage' and not as something accidental, as an instance of monstrosity. It is fully in ac- 

 cordance with what has been going on for ages within the calycinal system, through 

 long series of succeeding species, only it is here carried a step farther, as though 

 leadiag into a new phase of the morphological labour. In Mesozoic time the excretory 

 opening moved out of the system into the odd interradium, and was seen to increase 

 more and more the interjacent distance. After a while the madreporic filter followed 

 its track, attaining, near the close of Cretaceous time, the costal 5. With the aid of a 

 little imagination we might surmise that we actually witness how it exceeds the old 

 terminus and begins its exodus, and indulge in the idea that, in a future geologically 

 not very distant, the whole of the madreporite, in some species or other, will have 

 settled within the odd interradium, while the central disk, together with the costal 5, 

 cleared of the invading porosity, will have resuined their normal condition. Then 

 this gradual displacement of the madreporic filter, combined with other correlative 

 modifications of the external parts, accessory to internal changes of mOre directly vital 

 importance, will have originated a new type of Spatangidte. But this by the way, as 

 mere speculation. One point alone is established beyond any doubt by Avhat has been 

 detailed here, namely that in reality the madreporite is not an integral element of 

 the calycinal system, but an extraneous accessoiy, and that there exists no such thing 

 as a "madreporic plate». 



