Tue Microscope. 183 
an inch in diameter, and of irregular and inconstant form. 
Each consists of a speck of colorless protoplasm, the semi-fluid 
granular interior of which—the endosare pass into a firmer 
clear outer layer—the ectosarc. In the endosare, besides the 
nucleus there is sometimes a little cavity—contractile vesicle 
—endowed with the power of rhythmic dilation and contrac- 
tion. The sarcoid has the power of changing its form by the 
protrusion of blunt processes—from any part of its body, and 
when free from the mass it can crawl about by the same means. 
It bears, in fact, a remarkably close resemblance to an Amceba. 
In various parts of the canals, especially near the surface of the 
sponge, there are found round or oval chambers, lined with a 
layer of sarcoids, which present some advance in structure on 
the amcebiform type. Their form is usually columnar or oval, 
they possess nuclei and contractile vesicles, and their outer 
layer frequently assumes the character of a distinct limiting 
membrane. Each possesses a long f#agellum (Lat. for whip), 
which it is capable of lashing backwards. In many forms the 
limiting membrane is raised up round the base of the flagellum 
into a membranous collar, and the sarcoid very closely resem- 
bles certain collared imfusoria. Occasionally very peculiar 
forms are met with, where the flagellum and collar are borne 
at the end of a long neck. We can now understand that the 
currents which traverse the sponge are caused by the co-ordi- 
nated lashing in one direction of the flagella in these ciliated 
chambers, as they are called. But how is this co-ordination 
brought about? We do not know. It is one of the mysteries 
of protozoic life. Generally on the outside of the sponge, and 
less constantly in various parts of the interior, masses of nucle- 
ated protoplasm occur, which present a variation from the 
amcebal type in the opposite direction to that taken by the fla- 
gellated sarcoids, which we have seen is one of elaboration and 
specialisation. The masses in question present a degradation 
of structure, for the sarcoids of which they originally consisted 
have lost all their individuality, and fused into a continuous 
film, or syncytium, as Haeckel ealls it, and all that remains to 
mark their presence is their nuclei, but the mass still retains 
its functional activity.—Cole’s Studies. 
