INTEOUUCTION. 
15 
swarm-cells show that Ceratiomyxa belongs in essential pomts to 
the Mycetozoa, but with modifications in the intermediate stages 
of development. 
As has been stated before, many species of the Mycetozoa are 
associated with numerous varieties, using the word spectes as a 
name given for the convenience of classification to a form 
possessing definite and permanent characters which distinctly 
separate it from any other ; and the word variety to such as are 
linked with the type by a close series of connecting forms, and 
although more or less stable, do not possess such distinctive 
characters as would render it expedient or helpful to mark them 
with specific rank. 
The geographical distribution of most of the species is very 
wide, and the main characters are remarkably constant in 
specimens gathered in all parts of the world. 
Specimens of Eemitrichia davata, H. Serpula, Diciydiuvi umbi- 
licatum, and Trichia fallax, obtained from Europe, India, and 
North and South America, are identical to the most minute micro- 
scopic detail ; and numerous other equally stable forms might be 
cited. On the other hand, the American and tropical species of the 
genus Crihraria are more elegant in form than individuals of the 
same species here and on the Continent, and most of them show a 
tendency, in the great regularity of their structure, towards the 
type of C. intricata, a striking and well-marked species which is 
abundant in those regions, but rare in our less brilliant atmo- 
sphere. The genus is largely represented in America, and inter- 
mediate forms between the recognised species are frequent ; some 
of these are described by Dr. Rex in letters to me as being 
constant in gatherings from several States, but they are so 
closely allied to established types that he hesitates to give 
them separate specific names. The more elegant growth in the 
American species is not confined to the genus Crihraria, but 
is of general occurrence ; and it is probable that the slight 
modification of the prevailing type is due to the influence of 
climate. This is what might be looked for when we consider 
the efiects which changes of weather produce in the develop- 
ment of sporangia in this country. On old decaying stumps 
which can be kept under observation for several years, we may 
have gi'owths of Trichia affinis, which year after year present 
the same typical characters, only difiering in the elaters 
in one season being slightly thicker than those in another. 
When cold weather sets in while the plasmodium is rising, the 
arrangement of the spiral bands is so abnormal as to suggest a 
marked variety, but with a return of milder weather the oiiginal 
form reappears, leaving no doubt that all have been derived from 
a common parentage. Developments of Trichia j)ersi7nilis of the 
typical form have been followed after a few nights' frost by a 
growth in which the short and nearly smooth elaters clos?ly 
resemble those of Oligonema nitens, though the spores and the 
shape of the sporangia retain the normal character. T. scabra 
