CALCAREOUS SKELETON OF THE ANTHOZOA. 519 



together in a maimer wliicli will be best understood by refer- 

 ence to fig. 20. The cells are very irregular in shape, and are 

 separated from one another by considerable spaces. Some of 

 the cells nearest to the edges of a group appear to be under- 

 going disintegration. In these groups of calicoblasts two 

 other kinds of elements may be distinguished. The first kind 

 comprises the " ovoid bodies/' which I have already described 

 in Alcyonium digitatura. These bodies, which form a 

 constant element among the calicoblasts of Heliopora, do 

 not differ in any essential particulars from the similar bodies 

 in Alcyonium, except that, as is shown in fig. 14, some of 

 them show a distinct vacuolated structure. Though I have 

 devoted much time to them, I have been unable to throw any 

 light on their history or function; they may frequently be 

 observed in close association with the mesogloeal processes 

 which I am about to describe (vide fig. 18). 



Amongst the calicoblastic groups structures such as are 

 represented in fig. 15 constantly occur. They consist of a 

 much vacuolated cell with a nucleus and central contents, 

 stained blue with picro-nigrosin, and exhibiting a concentric 

 striation which may be due to the presence of a feltwork of 

 fibrill^. These are the earliest stages of structures which are 

 clearly homologous with the striated calicoblasts of von Heider. 

 They are shown in a somewhat later stage of development in 

 fig. 16, and in later stages in figs. 17, 18, and 19. In fig. 16 

 two such structures are shown : one is so placed that its 

 nucleus is clearly visible ; there is no longer any trace of the 

 surrounding layer of vacuolated protoplasm, and it appears as 

 an ovoid body with contents feebly stained by picro-nigrosin 

 and traces of striation. The other has no nucleus— probably 

 it was not included in the section, — but it has a clearly 

 defined striation along its lower margin, the striae in this case 

 being stained by the picro-carmine. It is noticeable that both 

 the structures lie outside of the layer of calicoblasts. Fig. 17, 

 which is an optical section drawn from a flat preparation, 

 shows a further stage of development of one of these structures, 

 which I shall henceforth call desmocytes. The previously 



