PLATE 1 



EXPLANATION OF FIGURES 



All figures are from Metridium (Actinoloba) marginatum Milne-Edwards. 

 Figures 1 to 3 are semidiagrams; figures 4 to 7 are camera drawings. 



ABBREVIATIONS 



ak., aeontium ms'gl., mesoglea 



cvl., mesenteric convolution mu.lg., longitudinal muscle 



ec'drm., ectoderm mu.t., transverse muscle 



en'drm., entoderm n'fbrl., neurofibril 



fil., mesenteric filament spht., sphincter 



go., gonad stm., oral stoma 



lab. lip stm'., marginal stoma 



ms'enr., mesentery 



1 to 3 Semidiagrams of mesenteries as seen in dissected specimens that had 

 been anesthetized with magnesium sulphate and hal-dened in 5 per cent formal- 

 dehyde in sea-water. In each drawing the oral end of the mesentery is upper- 

 most and the oesophageal edge is toward the left. Natural size. 



1 A directive mesentery. 



2 A non-directive, complete mesentery; the marginal stoma, usually single, 

 is represented by two holes. 



3 An incomplete mesentery showing the maximum number of organs present 

 on such mesenteries. 



4 Column wall seen in horizontal section; stained with Mayer's acid carmine; 

 the mesoglea, the only part in which the detail is drawn, contains many cells 

 as indicated by the numerous nuclei. Magnification 100 diameters. 



5 to 7 Drawings from three preparations showing neurofibrils stained by 

 the Titus method; magnification 100 diameters. 



5 Column wall seen in horizontal section; the neurofibrils in the mesoglea 

 of the column are seen passing into the mesogleal axis of a mesentery; the neuro- 

 fibrils show branching and, at the base of the mesenteric mesoglea, some fibrils 

 penetrate the entoderm in the region of the parietal muscles. 



6 Column wall seen in horizontal section; branching neurofibrils occur in 

 the mesoglea. 



7 An incomplete mesentery seen in horizontal section in the region of its 

 longitudinal muscle; its mesoglea contains many neurofibrils which enter the 

 entoderm where the longitudinal muscle-fibers are located; some of the neuro- 

 fibrils apparently terminate here in small knobs. 



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