10 Miss M. M. Ogilvie. Microscopic and Systematic [Nov. 21, 



(3) Changes of disintegration and crystallisation still continue 

 after the cell lamella has severed living contact with the polyp. The 

 disintegration of organic cell-remnants produces various flecks and 

 bands, usually carbonaceous, in the midst of the crystalline deposit. 

 These afford the explanation of the so-called " dark streaks " and other 

 ^appearances in the skeleton. 



The finer structure of the septa will be readily understood when it 

 is remembered that the septa are formed within radial invaginations 

 of the aboral body- wall of the polyp. The septal surfaces are prac- 

 tically casts of the two flaps of a septal invagination. When the 

 flaps are smooth, the calcareous lamellae are also smooth. But, 

 according to the author's observations, that is seldom the case in 

 recent Madreporaria. "Usually the septal flaps are pitted and goffered, 

 resembling the pleated muscular flaps of the mesenteries, and the 

 septal surfaces are correspondingly granulated and fluted. The author 

 has found that in all cases the calcified calicoblasts of successive 

 lamellae are grouped around definite centres of deposit situated in the 

 median plane — corresponding to the growing edge — of the septum. 

 ■Subsequently the individual groups of calicoblasts assume the form 

 of radiating bunches of fibro-crystalline aragonite, passing outwards 

 from the original centre of deposit in the median plane to the sur- 

 face of the septum. The author has given the name of "fascicles" 

 to these fibro-crystalline " bunches," and has demonstrated the re- 

 lation which they bear to the external sculpturing observed on lateral 

 septal surfaces. The emergence of a fascicle at the surface gives rise to 

 <a granulation. The fascicles are, however, of varied size ; if large, one 

 fascicle usually corresponds to one granulation; if small, a number 

 of fascicles may in the course of septal thickening coalesce to form 

 a broad nodular granulation. The size of individual fascicles depends 

 on the original closeness of the "centres of calcification" at the 

 septal edges. 



The trabecula (= " poutrelle " Edw. and H.) of a "perforate" 

 septum is composed of symmetrical groups of fascicles placed in vertical 

 series. The author has further found that those septa described by 

 Edwards and Haime as " imperforate and leaf -like " are also composed 

 of trabecule. But the individual parts of these trabeculae have an 

 opposite pair of fascicles instead of an indefinite number. The 

 majority of Astraeid genera have septa in which both kinds of 

 trabeculae occur. The author applies the term " simple trabecula " 

 to a trabecula made up of successive pairs of fascicles, as the axis of 

 deposit is in part or wholly common to the opposite fascicles ; and 

 the term " compound trabecula " to one made up of successive groups 

 of fascicles. In the former case the fibro-crystalline deposit may 

 be said to be bilaterally symmetrical in the opposite halves of a 

 septum ; in the latter the fibro-crystalline deposit is radially symme- 



