32 A Monograph of the Myxogastres. 



in advance of the one from which it emanated in an incipient 

 condition; hence in the Peritricheae, starting with the genus 

 Tubulina, the marked characteristic of the order a perforated 

 sporangial wall evolves gradually through Protodermium to 

 Dictydium, where it attains its highest phase of development, 

 and then terminates abruptly ; whereas in Enteridium, a com- 

 paratively primitive genus, we get a transition from slightly 

 perforated walls to a complete breaking up of their substance 

 into an irregular network, which leads by degrees to the central 

 columella and capillitium characteristic of the Columclliferae. 



PERITRICHEAE. 



The present order includes the most primitive types met with 

 in the Myxogastres, illustrated by such genera as Tubulina, of 

 which the plasmodiocarp condition, representing a plasmodium 

 covered by a common cortex, is the lowest phase ; when the 

 substance of the plasmodiocarp becomes broken up into smaller 

 portions by special walls, an aethalium is produced, and finally, 

 by the gradual isolation of the components of an aethalium we 

 get the sporangium or most highly specialized form of repro- 

 ductive organ, characteristic of the higher sections; but we 

 everywhere meet with plasmodiocarp and aethalioid conditions, 

 proving the comparative instability of the acquired sporangial 

 phase. In the present order we learn that the primitive idea 

 in connection with spore dissemination was that of modifying, 

 or rather differentiating, the sporangial wall. The original 

 function of the wall was protective, as illustrated in the genus 

 Tulnlina, where we find this to be its only function, there being 

 no provision for spore diffusion other than that brought about 

 by the decay of the wall, which does not take place readily, and 

 the subsequent dispersion of the spores by wind or rain. 

 Passing on to such genera as Enteridium and Clathroptychium, 

 we find the sporangial wall yet performing, as it continues to 

 do in every section, the function of protection, and remaining 

 intact until the spores are fully differentiated; but in these 

 genera certain portions of the wall have become specially 



