SPONGE. 281 
when free from the mass it can crawl about by the same means. 
It bears, in fact, a remarkably close resemblance to an Ameeba, 
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 simple 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 flage//um (Lat. for whip) which 
it is capable of lashing backwards and forwards. In many forms 
the limiting membrane is raised up round the base of the 
flagellum into a membraneous collar, and the sarcoid very closely 
resembles certain collared infusoria. 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 transverse the sponge are caused by the co-ordinated 
lashing in one direction of the flagella in these cedzated 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 nucleated protoplasm occur, 
which present a variation from the amoebal type in the opposite 
direction to that taken by the flagellated 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 syzcytium, as Haeckel calls it, and 
all that remains to mark their presence is their nuclei, but the mass 
still retains its functional activity. 
In some very few sponges (Myxospongiz) there is no skeleton, 
In the others the skeleton is usually strengthened, and, in some 
cases, entirely formed, by spiculze of carbonate of lime or silica. 
These spicule are of most varied and beautiful forms; if the 
reader wishes to see what a great variety there is, he must be 
referred to Bowerbank’s splendid monograph, published by the 
Ray Society, in which he will see two or three hundred distinct 
forms beautifully figured, and if he has nothing else to keep him 
out of mischief, he may occupy himself by learning by heart the 
two or three hundred names invented for their designation. Just 
to incite him to this study we quote three of these names—Exflected 
elongo-equiangulated triradiate, Furcated attenuato-patento-ternate, 
Torqueato-tridentate inequi-anchorate. We confess with all humility 
that we have not these terms at our fingers’ ends. It is evident 
that these spicule must tend to the preservation of the species 
possessing them, for by rendering them altogether unsuitable for 
the purpose of man, they are protected from his depredations, and 
