14 G. LINDSTRÖM, HELlOLlTlt)^. 



B)' these two different modes of growth we learn, first that the calicle of a Helio- 

 litidean does for some time exist without any coenenchyma and secondly that this structure 

 is a secondary growth and developed either from one side of the initial polypierite or 

 all around a calicle, which by rising as a tuba above the parent coenenchyma introduces 

 the intracalicinar geramation and thus for a time exists as a portion of a solitary indivi- 

 dual. Consequentlv it belongs not exclusively to a compound coral. It acquires its cha- 

 racter of a coenenchyma only Avhen it embraces more calicles than the first, when such 

 have been produced by it through gemmation. Before this happens it is something else. 



It can be shown that the perfect homology to it is found in corals which never 

 form compound corals, but contiuue single through their life. The figure 25 pl. xii 

 represents the calicle of a Thecopsammia enlarged. The exteriör ends of the numerous 

 septa are dissolved into the dense, spinous and porous tissue which like a broad frame 

 surrounds them and the interiör of the calicle. This outer zone has been called wall by 

 DuNCAN but I think that it is a structure quite out of the category of a wall. It is in in- 

 timate connection with the septa and there is moreover outside this zone an epitheca or 

 rather a thin wall, because there seems indeed to be no real difference between these 

 two names and I do not think that any one has reaJly seen an epitheca covering a theca, 

 so as to make out the difference between the two in juxtaposition. The calicle of many 

 corals, recent and fossil, belonging to widely distant families, is in the same manner as 

 this Thecopsammia provided with a broad marginal, flat plane from which the septa radiate 

 towards the centre of the calicle. I have formerly ^ called this expansion »Gebräme», which 

 word may be rendered in English with börder or border-zone. I can not decide whether it in 

 some way is identical with the often employed term »Randplatte», but I should think that it is not. 



In several corals, as the palgeozoic Ptychophylla which resemble Fungia, the septa 

 are considerably dilatated exteriorly and form one of the largest borders. In the »Per- 

 forates» the outer ends of the septa vanish in the börder zone as in Thecopsammia and 

 Balanophyllia. If now a solitary coral of such a growth increases in width and then 

 propagates through gemmation, this latter procedure will take place on the börder. 

 A new calicle is budding out of this spongy, loose substratum, is surrounded hj a 

 quite similar porous börder and when at last several calicles have become placed in 

 the same way near each other, they coalesce with their borders to a common mäss, in 

 which the calicles project from the now fuUy developed coenenchyma. This consequently 

 arises from the coalesced borders of the calicles. It is the same with the HeliolitidEe. 



In the figure 26 pl. xii a young colony of a Turbinaria is delineated growing on 

 the surface of a dead coral of the same species. It is evident that the larger calicle has 

 sometime been alone, surrounded only by its reticulate and spiny börder, out of which 

 låter, when expanded sidewards, a new calicle has budded. 



To apply this to the coenenchyma of the Heliolitida? let us recapitulate and finish 

 the description of the structure of an individual polypierite in that family. Its component 

 parts are enclosed within a solid, imperforated wall. There cannot be the least doubt 

 thfit the theca is the first formed part and that it for a while alone constitutes the whole 



1 RrcHTHOFEN's Chiiia, Bd 4, p. .^9. 



