A. E. HILTOX ON CAPILLITIA OF MYCETOZOA. 11 



tubular air-passages with expansions at the axils, and numerous 

 free, distended ends. Secretions from the plasm are discharged 

 into these air-passages, and these deposit a very delicate mem- 

 branous lining characterised by many wrinkles, which are 

 afterwards, no doubt, accentuated by shrinkage in drying. 



In the well-known genus Stemonitis the stalk is continued 

 upwards as a columella nearly to the apex of the tall sporangium, 

 and from this central columella, throughout its entire length, 

 the capillitium branches in all directions, combining into a loose 

 network, and becoming finer towards the periphery, until the 

 ultimate branches unite in forming a delicate surface net. The 

 outside of the net is covered with a frail membrane which con- 

 stitutes the ephemeral sporangium wall; and after this has 

 broken away, the spores escape through the meshes. 



It is interesting to compare the surface-nets of Stemonitis 

 with sporangial features of Cribraria and Dictydium. In these 

 two genera the cavity is entirely filled with spores ; and it is 

 xisually said there is no capillitium, because there are no threads 

 in the interior. The sporangium walls, hoM^ever, although more 

 or less firm at the base, are for the most part membranous and 

 evanescent ; and here again the breaking away of the membrane 

 reveals a surface-net with meshes which liberate the spores. 

 As these nets are continuous with basal structures, instead of 

 springing from a central columella, as in Stemonitis, they have 

 hitherto been regarded as persistent remains of the sporangium 

 walls ; but there is little doubt that in origin and composition 

 they are capillitial formations, as truly as the surface nets of 

 Stemonitis. 



The variations thus briefly described are only a few out of 

 many, but for our present purpose the examples given are 

 sufficient.* Biological interest in Mycetozoa is solely concerned 



* For a complete set of illustrations see Lister's Monograph of the 

 Mycetozoa, 2nd edition, revised, 1911. The plates in this work give 

 in each instance a figure of the capillitium as well as of the sporangial 

 forms/ 



