A NEW FIELD FOR THE MICROSCOPIST. 
123 
That sponges, taken as a whole, possess a something over 
and above what is encountered in the simple, independent, 
collar-bearing monad types cannot for a moment be denied. 
What the distinction is, and the extent to which it complicates 
or masks their true nature and affinities, may be briefly ex- 
plained. A sponge-body, cut through and examined with the 
microscope, though presenting at first sight an exceedingly 
complex type of structure, will be found on closer inspection to 
consist of a few very simple elements. Occupying, in the ma- 
jority of species, the largest, but by no means most essential por- 
tion of its composition, is the glairy, gelatinous sarcode, or syn- 
cytium, which forms, as it were, the basis or superstructure in 
and upon which all the other elements are distributed. Within 
its substance are imbedded, or, in fact, originated, when pre- 
sent, the various skeletal components, whether spicules, horny 
fibre, or a combination of the two, that give to the complete 
sponge that amount of rigidity or variety of contour that dis- 
tinguishes the various species. Abundantly scattered through- 
out the substance of this slimy matrix will likewise be found 
the amoebiform bodies of every shape and size to which the 
name of 66 cytoblasts ” has been latterly applied. Last and 
most essential of all are the collar-bearing flagellate monads or 
spongozoa, identical in form and structure with the independent 
collar-bearing species already introduced. These constituent 
sponge -monads most usually either line the entire surface of 
the inner cavities of the sponge, or occupy special spherical 
chambers within the same. These three living elements or 
factors now enumerated, namely, the glairy and structureless 
syncytium, the amoebiform cytoblasts, and the collar-bearing, 
flagellate monads, once intelligently recognized, the reduction of 
the sponge-structure to a still more simple formula is, with the 
light now afforded by a knowledge of the structure and deve- 
lopmental history of the independent collar-bearing types, a 
comparatively easy task. With such accessory light it may be 
shown, indeed, that the collar-bearing monads are the only essen- 
tial factors, and that towards them all the remaining structures 
occupy an entirely subordinate position. Given, in fact, a single 
one of these constituent monads, and a perfect sponge-body can 
in a little while be progressively built up. By a mucus-like 
exudation from its surface the basis of the syncytium is laid in 
a manner absolutely identical with the process by which the 
at first mucilaginous, but afterwards indurated lorica, or protec- 
tive sheath of the genus Salpingoeca is originated.* By a re- 
* Several higher ciliate infusorial forms produce a mucilaginous investing 
sheath by a similar process of exudation. In one of the most conspicuous 
of these, Ophrydium versatile , large colony-masses are formed containing 
