8 PERCY SLADEN TRUST EXPEDITION 



Mesoglsea. This name was employed by Bourne (11) to replace the term "meso- 

 derm " m denoting the supporting lamina of Coelenterates, since by usage " mesoderm " 

 had become identical with the mesoblast of the Triploblastica. The supporting lamina 

 has been described under various names : Milne Edwards and Haime refer to it as 

 the "tunique musculaire," the Hertwigs use the terms "mesoderm," " stutzlamelle," 

 " stiitzsubstanz," while among some English authors names like " supporting lamella " 

 (H. V. Wilson) and " structureless (or basement) membrane " (Gardiner) have been 

 resorted to ; McMurrich (100, p. 270) compared it with " the limiting membrane which 

 occurs just below the ectoderm " in the higher Metazoa. Bourne's new name was accepted 

 by Haddon (55) and van Beneden (8), and is now in common use among most English 

 and American authors (Hickson, McMurrich, Duerden, etc.). 



Lacaze Duthiers (92) and Faurot (40) have, however, questioned the necessity for 

 a new name in preference to the older term "mesoderm." The latter author, after careful 

 study, regarded it as composed of lamellee (" plissements "), which in Actinians are disr- 

 posed circularly in the body-wall and longitudinally in the mesenteries and are capable 

 of being separated from one another ; these lamellae could be dissociated still further into 

 fibrillse. The granulations on the mesenterial pleats (" feuillets ") seen in transverse 

 sections, which the Hertwigs (and others after them) regarded as the cut ends of the 

 endodermal muscle-fibres, are regarded as sections of " barbelures," which are part of 

 the intermediate substance. In a subsequent work (42) Faurot still adhered to the term 

 "mesoderm" for two reasons; "la lame mesodermique, bien que n'etant revetue qu'en 

 partie par des fibrilles musculalres, est contractile dans toute son etendue. Certaines 

 regions du corps, susceptibles de se contracter tres fortement, ne presentent sur les 

 coupes, aucune trace de ces fibrilles. Le disque pedieux notamment, en est completement 

 depourvu, et cependant certaines Actinies telles que V Actinia mesembryanthemum peuvent 

 se deplacer sans I'intervention des cloisons, a I'aide de ce disque. Les elements ecto- 

 dermiques musculaires dits "immerges" n'existent pas dans le mesoderme de la colonne 

 et cependant cette parol pent se contracter longitudinalement. Et d'ailleurs, un tissu 

 contractile doit-il necessairement, soit renfermer des elements musculaires, soit en etre 

 reconvert?" (p. 367); and again, " un autre motif pour ne pas renoncer, jusqu a present 

 chez les Actinies, a la designation de ' mesoderme ' c'est qu'il n'a pas encore ete formelle- 

 ment demontre que cette couche intermediaire n'est pas, en realite, chez ces animaux, le 

 premier rudiment d'nn veritable mesoderme. II me paralt certain d'ailleurs, ainsi qu'on 

 le verra par la suite de ce travail, qu'elle joue un tres grand role dans la formation du 

 pharynx, des cloisons, et aussi, fait remarquable, de certaines parties (loges) de la cavite 

 du corps" (p. 369). Faurot further suggested from certain observations on the changes 

 in the colour-markings of the tentacles of Peachia hastata and on the irregular size of 

 the " plissements " in the column-wall of Bunodes thallia that the contractility of the 

 mesoderm is amoeboid. In his latest paper (43, p. 347) he regards the usual view that 

 the supporting substance is a secretion of the ectoderm or endoderm as vague and not 

 based on accurate observation. 



At first the supporting lamella appeared to be a homogeneous substance which 

 uniformly stained in eosin or picro-nigrosin and did not contain any cell inclusions. 



