622 THE AMERICAN NATURALIST. (VoL. XXXIX. 
The young trophozoite may follow one of several lines of 
development. These lines diverge considerably. The nature 
of the forms so produced is indicated in the following table, 
which is taken from Doflein : — 
Group I. Free-living forms. 
Group II. Sedentary forms. 
I. Inclosed in cysts. 
2. In the state of *' diffuse infiltration." 
3. Cell parasites. 
Group I contains the most highly organized of the Myxospori- 
dia. Its members lead a free life in the gall bladder, urinary 
bladder, or kidney tubules of their hosts. They display differ- 
entiation into ectosarc and endosarc. The latter is essentially 
like that of other Sporozoa. The former is a clear granular 
layer. It is the seat of motion and gives origin to the pseudo- 
podia. A myocyte does not appear to have been described. 
Throughout these animals resemble the Rhizopoda. 
Group II is doubtless an offshoot from Group I, with the 
exception of the cell parasites. The encysted forms are those 
Which come to rest at some point within the host's body. The 
part thus attacked reacts by the formation of a wall around the 
parasite, which is thereupon prevented from extending its 
explorations.  * Diffuse infiltration " results when the parasite 
spreads out through a considerable region of the host's tissues. 
In such cases no cyst is formed. Eventually, these two kinds 
of trophozoites die as trophozoites, but leave the tissues which 
they had occupied, filled with spores. 
The forms hitherto considered are mostly animals of consider- 
able size, while the cell parasites, which belong to the suborder 
Cryptocystes, are amongst the smallest of the Sporozoa. The 
mode of life is, however, much the same. It is to this group 
that belongs the destructive Nosema (Glugea) bombycis, the 
cause of the silk-worm disease. | 
In no Myxosporidian is an intermediate host known, and 
infection is apparently always the result of chance. In those 
forms which live in such places as the gall or urinary bladder, the 
