HISTOLOGY OF ASTRAEIDS 113 



into a short, somewhat irrpgiilar eminence which may or may 

 not contain a nucleus. Subsequently, the protoplasm of this 

 projection becomes modified from its periphery inwards to the 

 middle lamina of the column-wall and specialized fibres appear 

 in it. At the attachments of mesenteries to the corallum, the 

 calicoblastic projections are usually larger and each of them 

 often contains more than one nucleus ; when their protoplasm 

 has been modified, the attaching structures become connected 

 with the middle lamina usually by means of narrow necks, 

 while elsewhere they are smaller and arise directly from the 

 middle lamina. In my preparations there is no indication 

 that these processes are at first formed in cellular elements or 

 ' desmocytes ' w^hich become subsequently connected with 

 the middle lamina by the modification of neighlDouring ' cells ' 

 of the calicoblastic layer, as Bourne described (p. 329), but 

 they are the result of a continuous change in the multinucleated 

 calicoblastic layer, the transformation of the protoplasm 

 beginning from its periphery and gradually extending inwards 

 to join the middle lamina. The processes are the parts that 

 project beyond the outer margin of the calicoblastic layer and 

 in which the specialized fibres he. These fibres are pronounced 

 towards the periphery of the processes, gradually becoming 

 fainter as they reach the middle lamina, and probably they 

 merge into the fibrils of the latter.^ 



Part of the middle lamina is formed entirely in the ecto- 

 derm, viz. the processes of attachment in the calicoblastic 



^According to Bourne in Caryophyllia Smithii, 'where a 

 desmocyte is about to be formed, one, two, or three nuclei become sur- 

 rounded with a mass of darker, finely granular protojjlasm. The next 

 phase is the appearance of a band-shaped or ovoid body in the centre 

 of the granular protoplasm which already shows faint signs of striation . . . 

 usually one nucleus remains in close association with this body ; the others 

 (if more than one combine to form the granular protoplasmic mass) 

 appear to be concerned in the formation of the mesogladal process which 

 will join the desmocyte to the mesogladal lamina. The striations next 

 become more defined, and the desmocyte, which was at first separate from 

 the mesoglada, becomes attached to it by a jjrocess developed, as it seems, 

 at the expense of neighbouring cells ' (pp. 528-9). (A desmocyte containing 

 more than one nucleus he regarded as a cell.) 



NO. 265 I 



