112 GEORGE MATTHAI 



wavy mibranched fibres, the network of branching fibres, and 

 the nuclei with the granular protoplasm in which they lie, are 

 comparable respectively to the white fibres, branching fibres, 

 and the so-called connective-tissue ' corpuscles ' ; the various 

 elements lie in a clear matrix in both cases. It is probable that 

 the branching fil)res in the middle lamina of coral colonies are 

 elastic like those of connective tissue. 



The possibility has not been excluded that the fibrous 

 strands of the ' epithelio-muscular ' or ' myo-epithelial ' cells, 

 so commonly figured in connexion with the liistology of 

 Coelenterates, might only be fibres of the middle lamina torn 

 apart with the adjacent parts of the ectoderm and endoderm 

 in the process of teasing. Such results are to be expected ; the 

 ectoderm, middle lamina, and endoderm are organically con- 

 tinuous. (In teasing, protoplasmic parts are sometimes 

 dissociated from the fibres of the middle lamina, as in Hickson's 

 figures 28 b-e of A 1 c y o n i u m d i g i t a t u m .) It is not 

 improbable that, as in the Astraeidae, these strands may 

 be of the nature of connective-tissue fibres, for, in figured 

 examples of epithelio-muscular cells, the nuclei, unlike their 

 position in plain muscular fibres of mammals, lie in the proto- 

 plasm extrinsic to the strands (16, PI. vi ; 18, PI. xxxix ; 

 3, PL xxvi). 



Bourne, H. Y. Wilson, Duerden, and others regarded the 

 middle lamina of the Madreporaria as a secretion of 

 one or both of the protoplasmic layers and ' not formed by the 

 direct metamorphosis of the ends of ectoderm or endoderm 

 cells ' (37, p. 198). The appearances in my various prepara- 

 tions, however, suggest that the middle lamina is formed by 

 modification of part of the protoplasm of the ecto-endoderm 

 into cementing substance and fibres, all or some of the nuclei 

 in the modified part of the protoplasm becoming the nuclei of 

 the lamina. The formation of the middle lamina is well seen 

 in the case of the processes of attachment which are formed in 

 the calicoblastic layer, stages in their development being 

 abundantly present in my preparations (figs. 13-15). Where 

 such a process is to be formed, the calicoblastic layer is raised 



