198 



Dr. Alex. Brown — On Solenopora. 



small size. In some specimens spaces can be seen whicli are the 

 remains of the former conceptacles of sporocarps or sporangia. 

 These cavities communicate with the exterior by means of a 

 number of canals. The latter are generally surrounded by 

 a number of cells having a different shape from the ordinary 

 tissue-cells of the thallus. Tbis is specially well seen at the 

 external apertures of the canals (Fig. 9), where the modified cells 



Fig. 9. — Part of roof of " conceptacle " decalcified, x 40 d. (after Kjellman). 



in question give rise to a rosette-like appearance. These conceptacles 

 may or may not be immersed in the general substance of the thallus. 

 If immersed, then a scar or a vacant space is left to tell of their 

 existence ; or, indeed, they may be replaced by new tissue, so that 

 no trace of the former conceptacle can be seen. 



Eegarding other forms of the Corallinese, it is necessary to mention 

 one or two points for comparison. In Corallina mediterranea there 

 is no concentric arrangement of the tissue-cells, as there is in 

 Lithothamnion. The cells, too, are larger than in the latter, and 



Fig. 10. — Long. sect, of the apical shoot of Corallina mediterranea. x 300 d. 

 (after Solms-Laubachj. 



are arranged as in that genus in parallel rows, save where some 

 ■ cell in one of the rows has two cells attached to its distal extremity 

 in a sub-dichotomous manner (Fig. 10). The last feature is, 

 however, characteristic of certain extinct forms of Lithothamnion, 

 according to A. Eothpletz (op. cit. supra p. 6). 



In Amphiroa exilis and Amphiroa rigida the concentric arrangement 



