— 
bo 
Sy) 
“I 
— 
XII.—On the Mode of Growth and Increase amongst the Corals of the 
Paleozoic Period, By H. Attryne Nicwotson, M.D., D.Sc, F.RS.E, 
Professor of Biology in the Durham University College of Physical Science. 
(Plate X VIL.) 
(Read 1st March 1875.) 
The mode of growth and increase amongst the Coralligenous Actinozoa in 
general has been more or less fully treated of by various observers, including 
such distinguished naturalists as Mrtne-Epwarps, and Haime, Dana, Martin 
Duncan, FRoMENTEL, AGassiz, and others. I do not, therefore, in the present 
communication propose to pass the whole of this subject in review, but rather 
to consider the general and special peculiarities of growth and non-sexual 
reproduction exhibited by the corals of the Paleozoic Period alone. Many of 
these peculiarities are of great interest, both from the stand-point of the paleeon- 
| tologist, and also as concerns the systematic zoologist, and they have not yet 
/met with all the attention they deserve. To carry out this inquiry, it will be 
| necessary first to consider the general phenomena exhibited by the Paleozoic 
| corals, as regards their mode of growth and increase. We may then examine 
| the bearing of these phenomena upon various points connected with the classi- 
| fication of these ancient corals, and more especially upon their generic and 
specific affinities and differences. Finally, we may briefly consider the relations 
\which exist between different parts of a compound corallum as regards their 
| growth, and their influence upon the ultimate form of the colony. 
















I. GENERAL MopgEs oF GROWTH IN THE PALOZOIC CORALS. 
The Paleozoic corals belong, as is well known, almost exclusively to the 
groups of the Rugosa and Tabulata, and it is with these, therefore, that we are 
chiefly concerned. The Yubulosa, however, are wholly Paleozoic, and the 
\Aporosa and Perforata are not altogether unrepresented. None of these three 
last-mentioned groups, as regards their Paleozoic representatives, exhibit any- 
thing in their mode of growth which is not shown by some member of the 
Rugose or Tabulate divisions, and they will, consequently, require nothing more 
‘than incidental mention. The general methods of growth and increase exhibited 
iby the Paleozoic corals, may be considered under the following heads :— 
A. Simple Calicular Gemmation.—This mode of increase has not been suffi- 



VOL. XXVII. PART IIL. 3 Q 
