KONGL. SV. VET. AKADEMIENS HANDLINGAR. BAND 32. N:0 I. 13 



The initial or pavent polypierite has a length of 0,6 millimeters from the tip to the 

 upper edge of the calicle and also a diameter of 0,6 mm. of the calicle. It is cornet- 

 shaped ^ galning rapidly in width from the obtusely pointed apex and is with its whole 

 length affixed to the theca of a rugose coral. A blackish, glossy epitheca covers the outside, 

 finely transversally wrinkled. It is evident that this young polypierite besides the epitheca, 

 if there is any, consists of a comparatively thick theca and that in the beginning there 

 are no septa. This is quite in accordance with the development of other Silurian corals, 

 as I have described elsewhere - and as I hope to describe more in full at another occasion. 

 In these the sceleton also is an empty tube without any traces of septa, which appear 

 only a little låter one by one. When von Koch says '" that the theca probably always 

 develops out of the septa, which unite with their exteriör ends, he apparently only 

 had the recent corals in view, being not aware of the proceedings amongst the palseo- 

 zoic ones. 



The smallest specimen of Hel. interstinctus which I have found with septa was a 

 little above one millimeter in length and had five septa developed on one side of the 

 nearly circular outline (Pl. i fig. 30). The tabulte, in the beginning much concave, are 

 not seen until higher up in the tube (Pl. i fig. 28). By longitudinal sections and also 

 by direct observation on such specimens as figured on Pl. i figs. 25 — 28, is seen that the 

 coenenchyma is commencing to develop only when the young primary polyp has gained 

 soraewhat in length and after the first septa have been secreted. It is to be remarked 

 that this reticulate tissue in its beginning neveris formed on the exteriör or upper side 

 of the polypierite but always on the lower edge of the calicle — that side on which it 

 during the first stage of growth is reposing, affixed to a substratum. After a while the 

 coral has abandoned the rampant mode of growth and continues in an erect direction. 



Further to elucidate the formation of the coenenchyma we have to contemplate a 

 peculiar variety of calicinal gemmation, which occurs on the surface of mature colonies of 

 Heliolites and other genera of the family. In the figures 34 i — iv pl. i, a series of sec- 

 tions is represented from one and the same calicle of Heliol. interstinctus showing its 

 gradual transforraations, of which more in detail below. Suflice here to say, that out of 

 the tubular calicle, which has raised itself above the coenenchyma, a new coenenchyma has 

 grown around its theca and that this coenenchyma becomes also circumscribed by a theca 

 so that in this stage the corallum has two thecas, one interiör and one exteriör theca. 

 The exteriör theca through the increasing growth of the polvpary envelops at last a great 

 number of calicles with their surrounding coenenchyma and coincides or is identical with 

 the thin film which generally has been called epitheca, but for which I would rather 

 propose the name coenotheca as it is the common integument or wall of all calicles in a 

 compound Heliolitidean coral. 



^ Bernard, Journ. Limi. Soc. Zool. pt xxvi, 1898, p. 498, calls this iuitium of Alveopora an epithecal 

 cup, but it is probable that this, like Heliolites and others, consists not only of epitheca but of several thin 

 linings within the epitheca. 



ä Ueber die Gattuug Prisciturben Kunth 1889 Bihang. Vet. Akad. Handl., Bd 15 Afd. IVn:rl9 p. 4; 

 and Beschreibung einiger Obersilurischen Korallen etc. 1896 p. 8, Taf. I fig. 9, 10, also p. 49, Taf. VIII 

 fig. 110. 



ä Biol. Centralblatt W^ Bd p. 588. 



K. Sv. Vet. Akad. Handl. Band 32. N:o 1. 2 



