12 G. LINDSTRÖM, HELIOLITID^. 



all as in Plasin. stella, the species which shows it most perfectlj^ It may be larger than the 

 diameter of the calicle and it raay dwindle away to the smallest dimensions as in Plasm. 

 heliolitoides, but upon closer inspection it may always be detected. 



A dififerent vei"tical structure occurs in the genus Propora. If sections as fig. 16, 17, 18 

 etc. pl. X are compared we find tliat amongst the coenenchymal lamellaB vertical rods are 

 embedded, tapering at both ends, narrow, without anj^ perceptible, microscopical structure. 

 These rods may be named bacilli in contradistinction to another class, the toaculi, about 

 which further on. These bacilli are always solitary and do not unite, as seen in the 

 transvei'se section of them (fig. 16, 17) where they stånd out as black, widely separated 

 points and their tops project above the natural surface of the corallum (fig. 12). The 

 toaculi again (pl. ix fig. 42, 44, 46, pl. x fig. 3, 4, 5) are stouter, short and have a 

 distinct microscopical structure. They are, to wit, composed of diminutive fibrillee, which 

 stånd out on all sides, directed upwards from a central axis, which in some is visible as 

 a white line, but generally is Avanting and really imaginary as these fibrillfe radiate 

 from a common starting point which has no peculiar structure, being only the in- 

 tei'ior extremities of the fibrillffi. In longitudinal sections, where they are so common, 

 they have a pinnate appearance, the fibrillae standing out on both sides like the beard of 

 a feather. They are dispersed among the convex lamellaj of the coenenchyma, remote 

 from each other (pl. x fig. 5) and their superior ends project as tubercles on the surface 

 of the coral (pl. x fig. 3). I am not prepared to say that these bacilli and baculi are 

 to be considered as spicula, but it is evident that they share their intimate structure 

 with the thecal and septal sceletons of the plurality of recent and fossil corals. 



Amongst the Plasmoporinas the genus Diploépora occupies a peculiar position. In 

 the oldest strata or in the youngest stages of growth the coenenchyma is of the distinctest 

 vesicular nature, quite as in the most simple Proporas, consisting only of convex lamella^. 

 But during the continued growth of the polypary (Pl. xi fig. 4) this sort of coenen- 

 chyma is supplanted by a quite dissimilar one, a dense stratum of baculi, closely packed 

 together and of the same pinnate structure as the solitary baculi just described. Though 

 sharing for the rest all the particulars of the other Plasmoporina? it really forms a tran- 

 sition to the next category of coenenchyma. 



3. The baciilar coenenchyma. The smal! tribe of the Coccoseridse has its coenen- 

 chyma composed of baculi (Pl. xi f. 33, Pl. xii f. 6) also of the general pinnate 

 structure. 



4. The compact coenenchyma. In the genus Pycnolithus (Pl. xi fig. 8, 9) the 

 coenenchyma is a dense, homogenous mäss, a little granular, longitudinally permeated by 

 white lines being vestiges of the replenished tubuli. 



In order to demonstrate the development of the coenenchyma of Heliolites and 

 to explain its nature I have had recourse to initial stages of colonies which have only a 

 few millimeters in length. Also a peculiar manner of gemraation of calicles on the sur- 

 face of the polyparies has given good information. I have as yet not succeeded in fin- 

 ding a single polypierite, just in its initial sta-ge, but, as shown pl. i fig. 25, one suffi- 

 ciently small incipient colony gives good idea of the first beginning. It consists of the 

 initial polypierite and of two others which have budded out from the coenencliyina. 



