the Giliate Infusoria. By G. J. Allman. 183 
ever, we must regard them as only differentiated protoplasm 
filaments. In the morphological conception of true muscle, its cell 
nature is absolutely indispensable. The so-called muscle fibrils of 
the Infusoria never show a trace- of nucleus. They can be viewed 
only as jparts of a cell due to the differentiation of the sarcode 
molecules of its protoplasm ; and as they are thus only sarcode 
filaments, Haeckel designates them by the term " myophan," as 
indicating a distinction from proper muscle. 
The trichocyst layer occurs also in many Infusoria, but not in 
all. It is a thin stratum of the exoplasm lying immediately on the 
endoplasm, and including in certain species the trichocysts. The 
presence of these bodies, which possess a striking resemblance to 
the thread-cells of the Coelenterata, has, as we have already seen, 
been urged as an argument in favour of the multicellularity of the 
Infusoria. But, as Haeckel argues, no evidence of multicellularity 
can be derived from this fact. The thread-cells of the Coelenterata 
are themselves the products of a cell, and we often find many of 
them originating in a single formative cell quite independently of 
the nucleus ; the formative cell may in this respect be compared 
with the entire body of the Infusorium. 
It is the endoplasm, or internal parenchyma of the Infusoria 
that has given rise to the most important differences of opinion, and 
in his account of this part of the Infusorium organism Haeckel 
chiefly directs his criticism against the views advocated by Claparede 
and Lachmann, and by Greeff. 
These authors, as we have already seen, compare the Infusoria 
with the Coelenterata, and regard the endoplasm not as a real part 
of the body, but merely as the contents of the alimentary canal — 
as a sort of food mash or chyme contained in a spacious digestive 
cavity whose walls are at the same time stomach wall and body 
wall, and into which the mouth leads by a short gullet. As 
Haeckel urges, however, it needs only a correct conception of the 
intestinal cavity throughout the animal kingdom and of its distinc- 
tion from the body cavity, in order to show the untenableness of 
this position. The main point of such a conception lies in the fact 
that the intestinal cavity and all extensions of it (gastro- vascular 
canals, &c.) are always originally clothed by the endoderm or inner 
leaflet of the blastoderm, while the body cavity is always formed on 
the external side of the endoderm, and between this and the 
ectoderm or outer leaflet of the blastoderm. The body cavity and 
intestinal cavity of animals are thus essentially different ; they 
never communicate with one another, and always arise in quite 
different ways. 
Again, the contents of a true intestinal cavity consist only of 
nutritious matter and water, in other words, of chyme ; while the 
fluid which fills the body cavity is never chyme, but is always a 
